Wanda's children were retconned to "not exist" until Young Avengers . . . which grew out of Avengers Disassembled, which was when Wanda was revealed to be god hax crazy enough to create an alternate timeline.
It could be that Tommy and Billy . . . are a result of Wanda's god hax crazy, and don't "really exist" the same way House of M doesn't exist.
Aaron "The Mad Whitaker" Bourque; I need to go to bed.