Customise authoryear or write a new style? [duplicate]

Question

I'm currently finishing up my thesis and have some troubles getting the citation style I want. I tried to customise the authoryear style in biblatex but it's my first time using latex so I can't seem to wrap my head around the code.

I only have two types of entries in my library: articles and two masterthesis entries. I usually import articles directly from PubMed to JabRef (and don't change anything in the entry)

MWEB:

 \documentclass{article}
            \usepackage[natbib=true,backend=biber,style=authoryear,firstinits=true,uniquelist=false]{biblatex}
            \addbibresource{\jobname.bib}
            \usepackage{filecontents}

            \begin{filecontents}{\jobname.bib}
        @Article{Gross2007,
          author   = {Gross, Stefan Alfred and Wissenbach, Ulrich and Philipp, Stephan Ernst and Freichel, Marc and Cavalié, Adolfo and Flockerzi, Veit},
          title    = {Murine ORAI2 Splice Variants Form Functional Ca2+ Release-activated Ca2+ (CRAC) Channels},
          journal  = {Journal of Biological Chemistry},
          year     = {2007},
          volume   = {282},
          number   = {27},
          pages    = {19375-19384},
          doi      = {10.1074/jbc.M701962200},
          eprint   = {http://www.jbc.org/content/282/27/19375.full.pdf+html},
        }
        @Article{Gwack2007b,
          author                 = {Gwack, Yousang and Srikanth, Sonal and Feske, Stefan and Cruz-Guilloty, Fernando and Oh-hora, Masatsugu and Neems, Daniel S. and Hogan, Patrick G. and Rao, Anjana},
          title                  = {Biochemical and functional characterization of Orai proteins.},
          journal                = {The Journal of biological chemistry},
          year                   = {2007},
          volume                 = {282},
          pages                  = {16232-43},
          address                = {United States},
          article-doi            = {10.1074/jbc.M609630200},
          article-pii            = {M609630200},
          completed              = {20070719},
          date-created           = {20070528},
          electronic-publication = {20070209},
          grantno                = {GM075256/GM/NIGMS NIH HHS/United States},
          issue                  = {22},
          language               = {eng},
          linking-issn           = {0021-9258},
          nlm-unique-id          = {2985121R},
          owner                  = {NLM},
          print-issn             = {0021-9258},
          publication-status     = {ppublish},
          registry-number        = {0 (Stromal Interaction Molecule 1)},
          revised                = {20161124},
          source                 = {J Biol Chem. 2007 Jun 1;282(22):16232-43. Epub 2007 Feb 9.},
          status                 = {MEDLINE},
          subset                 = {IM},
          title-abbreviation     = {J Biol Chem},
        }
        @Article{Berna-Erro2009,
          author   = {Berna-Erro, Alejandro and Braun, Attila and Kraft, Robert and Kleinschnitz, Christoph and Schuhmann, Michael K. and Stegner, David and Wultsch, Thomas and Eilers, Jens and Meuth, Sven G. and Stoll, Guido and Nieswandt, Bernhard},
          title    = {STIM2 Regulates Capacitive Ca\<sup\>2+\</sup\> Entry in Neurons and Plays a Key Role in Hypoxic Neuronal Cell Death},
          journal  = {Sci. Signal.},
          year     = {2009},
          volume   = {2},
          number   = {93},
          pages    = {ra67},
        }
        @Article{Wang2010,
          author   = {Wang, Youjun and Deng, Xiaoxiang and Mancarella, Salvatore and Hendron, Eunan and Eguchi, Satoru and Soboloff, Jonathan and Tang, Xiang D. and Gill, Donald L.},
          title    = {The Calcium Store Sensor, STIM1, Reciprocally Controls Orai and Ca(V)1.2 Channels},
          journal  = {Science (New York, N.Y.)},
          year     = {2010},
          volume   = {330},
          number   = {6000},
          pages    = {105--109},
          issn     = {1095-9203},
          comment  = {20929813[pmid]},
          database = {PMC},
        }
        @Article{Park2010,
            author   = {Park, Chan Young and Shcheglovitov, Aleksandr and Dolmetsch, Ricardo},
            title    = {The CRAC Channel Activator STIM1 Binds and Inhibits L-Type Voltage-Gated Calcium Channels},
            journal  = {Science},
            year     = {2010},
            volume   = {330},
            number   = {6000},
            pages    = {101},

        }
            \end{filecontents}

            \begin{document}

            \citep{Gross2007,Gwack2007b,Berna-Erro2009}.
           \citep{Wang2010,Park2010}.


            \printbibliography

            \end{document}

This code gives me this:

I do however would like my bibliography to look like this

I want to show all author names, in this order : lastname, Initials of first names. When there are more than six authors, after the sixth author the rest should be abbreviated with et al.

Also with the citations in the text I do face some problems I wasn't able to recreate for a MWEB:

So sometimes the first initial of the first author is printed:

I use the natbib-comp mode (because I started of with bibtex and then switched to biblatex) so I want my citations to look like this:

(AuthorA et al., year; AuthorB et al., year) (AuthorA und AuthorB, year) each time only showing the last name and no additional initials of the first name!

If there are more than 3 authors, it should be abbreviated with et al. after the first author.

Thanks for any help!