I don't really exactly know how to be a co-founder like accepting someone's art in the group, but idk if there's supposed to be a button for accepting it, but for me it only says withdraw.
It's ok... When I started on DA (when I was W-w-pony) I had a lot of pony pictures of my Pony OC's but I will remember both my past accounts on DA... I even forgot what the group was called on W-w-pony (soz... I was only talking about my past... I started 2014)