The immediate problem that comes to mind re twins as Superman/Clark is--why invent Superman? Superman is an identity invented to protect Clark's normal life. If Clark has a twin brother who is always Superman and never Joe Regular, then poor Joe never gets a normal life.
The obvious way to solve this is to have the twins take turns being Clark Kent *and* Superman, which kills the Lois choosing between Clark and Superman idea, but adds even more "You are in such deep doo-doo when Lois finds out what's really going on" potential. Especially if only one of them is in love with Lois.
It also makes it harder for Lois to figure it out on her own, because she will see Superman and Clark together from time to time, and Clark won't have to make awkward exits because one of him will always be on Superman duty. Then again, there must be some disasters in which *two* Supermen are better than one, and could the "off duty" Clark really stay away in such a case?
Just thinking out loud.
