I'll admit I'm not deeply familiar with most religious traditions, but I am absolutely sure none of the major ones have any "tradition" in which Jesus had a twin brother. Yes, "Thomas" means "the twin," but not because people believed he was actually Jesus' twin brother.
It's hard for me to take any of the summaries seriously after that, and it's almost enough to make me wonder whether the collection would actually include accurate copies of the documents it claims to.