Bold labels and more with custom bibtex bst and author-year

Question

I have the requirement to print the labels for the entries in the bibliography in bold, replace the , between multiple authors (if any) with ; and end them with :. The following picture is an example from my guidelines:

I suppose that should be possible by modifying my custom .bst file and especially the format.names function. Based on this and this I came up with the following function:

FUNCTION {makebold}{
{ duplicate$ empty$
    { pop$ "" }
    { "\textbf{" swap$ * "}" * }
  if$ 
}

However, when I add it to my bst file I only get compilation errors without even calling the function, just by copying it into the file.
This is my current format.names function.

FUNCTION {format.names}
{ 'bibinfo :=
  duplicate$ empty$ 'skip$ {
  's :=
  "" 't :=
  #1 'nameptr :=
  s num.names$ 'numnames :=
  numnames 'namesleft :=
    { namesleft #0 > }
    { s nameptr
      "{vv~}{ll}{, jj}{, f{.}.}"
      format.name$
      bibinfo bibinfo.check
      't :=
      nameptr #1 >
        {
          nameptr #2
          #1 + =
          numnames #2
          > and
            { "others" 't :=
              #1 'namesleft := }
            'skip$
          if$
          namesleft #1 >
            { ", " * t * }
            {
              s nameptr "{ll}" format.name$ duplicate$ "others" =
                { 't := }
                { pop$ }
              if$
              "," *
              t "others" =
                {
                  " " * bbl.etal *
                }
                { " " * t * }
              if$
            }
          if$
        }
        't
      if$
      nameptr #1 + 'nameptr :=
      namesleft #1 - 'namesleft :=
    }
  while$
  } if$
}

I have no experience with bst files at all, but need this fixed, because my instructor is already complaining that I should use Word instead of LaTeX and he will force me to migrate my paper if I can't sort out his beloved bibliography style :(

It would be really nice if someone could help me print my entries the way they should be!
Last remark: don't know if that's relevant, but the names should not be bold in the text like when I'm using \citep etc.

Update: I've managed (with pure trial and error) to get the labels bold (I had to rename the function to bolden instead of makebold, don't know why) and replace the comma between authors with a semicolon. What's still missing is the final colon between the author list and the title.
My current format.names looks like that:

FUNCTION {format.names}
{ 'bibinfo :=
  duplicate$ empty$ 'skip$ {
  's :=
  "" 't :=
  #1 'nameptr :=
  s num.names$ 'numnames :=
  numnames 'namesleft :=
    { namesleft #0 > }
    { s nameptr
      "{vv~}{ll}{, jj}{, f{.}.}"
      format.name$ bolden
      bibinfo bibinfo.check
      't :=
      nameptr #1 >
        {
          nameptr #2
          #1 + =
          numnames #2
          > and
            { "others" 't :=
              #1 'namesleft := }
            'skip$
          if$
          namesleft #1 >
            { "; " * t * }
            {
              s nameptr "{ll}" format.name$ duplicate$ "others" =
                { 't := }
                { pop$ }
              if$
              "" *
              t "others" =
                {
                  " " * bbl.etal bolden *
                }
                { "; " * t * }
              if$
            }
          if$
        }
        't
      if$
      nameptr #1 + 'nameptr :=
      namesleft #1 - 'namesleft :=
    }
  while$
  } if$
}

Answer 1

Here is a code using biblatex that seems to fulfill the requirements:

        \documentclass[german]{article}%mkbib
        \usepackage[T1]{fontenc}
        \usepackage[utf8]{inputenc}
        \usepackage{lmodern}
        \usepackage{babel}%
        \usepackage{csquotes}
        \usepackage{xpatch}
        \usepackage[backend=biber, style=authoryear, firstinits, mergedate=false]{biblatex}

        \addbibresource{marcedb.bib}
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        \renewcommand*{\multinamedelim}{\addsemicolon\space}
        \renewcommand*{\subtitlepunct}{\addcolon\space}
        \renewcommand*{\newunitpunct}{\addcomma\space}
        \renewcommand*{\finentrypunct}{\addperiod}
        \renewcommand*{\revsdnamepunct}{\addcomma\space}%
        \renewcommand*{\finalnamedelim}{\multinamedelim}
        \renewcommand*{\mkbibnamelast}[1]{\textsc{#1}}%
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        \DeclareNameAlias{sortname}{last-first}
        \DeclareNameFormat{last-first}{%
          \iffirstinits
            {\mkbibbold{\usebibmacro{name:last-first}{#1}{#4}{#5}{#7}}}%
            {\mkbibbold{\usebibmacro{name:last-first}{#1}{#3}{#5}{#7}}}%
          \usebibmacro{name:andothers}}

        \renewcommand*{\labelnamepunct}{\bfseries\addcolon\space}

        \renewbibmacro*{date+extrayear}{}%

        \renewbibmacro*{date}{%
        \mkbibparens{\printdate}}%

        \renewbibmacro*{issue+date}{%
                \printtext{\usebibmacro{date}}
                \setunit*{\addcomma\space}
                \printfield{issue}
         \newunit}

        \renewbibmacro*{series+number}{%
         \addcomma\space
         \iffieldundef{series}{}{\printtext[parens]{\printfield{series}%
          \setunit*{\addsemicolon\space}%
          \printfield{number}}}%
          \newunit}

        \renewbibmacro*{publisher+location+date}{%
          \printlist{location}%
          \iflistundef{publisher}{}%
          {\addspace\printtext{u.a.:}}
          \printlist{publisher}%
          \addspace%
          \usebibmacro{date}%
          \newunit}

        \xpatchbibmacro{byeditor+others}%
        {\usebibmacro{byeditor+othersstrg}%
             \setunit{\addspace}%
             \printnames[byeditor]{editor}%
             \clearname{editor}%
             \newunit}%
        {\printnames[byeditor]{editor}%
             \clearname{editor}%
             \setunit{\addspace}
             \mkbibparens{Ed\addperiod}%
             \newunit}%

        \xpatchbibdriver{inbook}{%
          \newunit\newblock
        \usebibmacro{maintitle+booktitle}%
          \newunit\newblock
          \usebibmacro{byeditor+others}}%
          {%
          \iffieldundef{bybookauthor}{}%
         { \newunit\newblock}%
          \usebibmacro{byeditor+others}%
          \setunit{\addcolon\space}\newblock
          \usebibmacro{maintitle+booktitle}}%
          {}{}%

        \renewbibmacro*{journal+issuetitle}{%
          \usebibmacro{journal}%
          \setunit*{\addcomma\space}%
          \iffieldundef{series}
            {}
            {\newunit
             \printfield{series}%
             \setunit{\addspace}}%
          \usebibmacro{volume+number+eid}%
          \setunit{\addspace}%
          \usebibmacro{issue+date}%
          \setunit{\addcolon\space}%
          \usebibmacro{issue}%
          \newunit}

            \begin{document}

             \nocite{*}
              \printbibliography

            \end{document}

and the result:

Answer 2

Alright, I was able to fix the problems :) I'll post the solution here in case someone else stumbles about the problem in the future.
Three steps are required. First, this is the correct format.names:

FUNCTION {format.names}
{ 'bibinfo :=
  duplicate$ empty$ 'skip$ {
  's :=
  "" 't :=
  #1 'nameptr :=
  s num.names$ 'numnames :=
  numnames 'namesleft :=
    { namesleft #0 > }
    { s nameptr
      "{vv~}{ll}{, jj}{, f{.}.}"
      format.name$ bolden
      bibinfo bibinfo.check
      't :=
      nameptr #1 >
        {
          nameptr #2
          #1 + =
          numnames #2
          > and
            { "others" 't :=
              #1 'namesleft := }
            'skip$
          if$
          namesleft #1 >
            { "\textbf{;} " * t * }
            {
              s nameptr "{ll}" format.name$ duplicate$ "others" =
                { 't := }
                { pop$ }
              if$
              "" *
              t "others" =
                {
                  " " * bbl.etal bolden * 
                }
                { "\textbf{;} " * t * }
              if$
            }
          if$
        }
        't
      if$
      nameptr #1 + 'nameptr :=
      namesleft #1 - 'namesleft :=
    }
  while$
  } if$
  ": " bolden *
}

This is a working bolden method:

FUNCTION {bolden}
{ duplicate$ empty$
    { pop$ "" }
    { "\textbf{" swap$ * "}" * }
  if$
}

Step two is to add output.nonperiod after the format.authors call in an entry function to remove an additional dot.

FUNCTION {article}
{ output.bibitem
  format.authors output.nonperiod "author" output.check
  author format.key output
  new.block
  format.title "title" output.check
  new.block
  crossref missing$
    {
      journal
      "journal" bibinfo.check
      "journal" output.check
      format.vol.num.pages output
      format.date "year" output.check
    }
    { format.article.crossref output.nonnull
      format.pages output
    }
  if$
  format.issn output
  new.block
  format.note output
  format.eprint output
  fin.entry
}

Step three is the most annoying part: Repeat step two for every entry you are using.

This isn't a nice or clean solution, but the hack does what I need it to do, so I'm satisfied for the moment :)

Edit: Just for completeness, Bernard's answer should be preferred. I forgot to add the nonperiod methods here:

FUNCTION {output.nonperiod.nonnull}
{ 's :=
  write$
  s
}
FUNCTION {output.nonperiod}
{ duplicate$ empty$
    'pop$
    'output.nonperiod.nonnull
  if$
}