They're called the Stepford Cuckoos because they're an amalgamation of The Stepford Wives and The Midwich Cuckoos (better known to movie goers as Village Of The Damned).
Weapons XIII, XIV, and XV in New X-Men were created in The World, where Sublime was playing with relative time to speed up natural evolution and create the better Mutant-killer; so while there may be Emma Frost and/or Steve Rogers DNA in the Cuckoos, it would be many, many generations back.
Well, originally. God only knows what it is now.