Okay, everything is sorted out. Something someone said to me a while back got the multiverse confused in my head, because they were mixing up dimensions and multiverses. Since I hadn't read about the multiverses and how they were formed for a while so it wasn't fresh in my head, what they said really really confused me and caused some problems in this thread. Everything is sorted now and back on track. Please disregard everything above accept for the first post. I'm very sorry for the confusion.
LordMing and I have been talking, and we've decided to go with a new dimension since that gives us total freedom of creativity, and an explanation of why and how it exists isn't needed. We're picking different things and versions of characters from different multiverses. Just now, for the sake of balance of powers (three kryptonians being too many) we've gone with Superman, Power Girl (Kara Zor-L), and Linda Danvers as Supergirl. I also think Linda Danvers is a good choice since a character I'm playing has strong ties to the theme of demonology in the DC Universe. I guess pretty soon we'll need to make a new thread.