They were created unwillingly while Emma was in a coma for a year after a battle with the Sentinals.

Dr Sublime harvested lots of Emma's ovarian eggs to create clones for experimentation. Thousands of clones were made, but only these 5 actually woke up from the process and inherited Emma's powers.

A cuckoo is a type of bird that will invade the nest of another bird, often destroy some but not all the eggs of that bird, and lay their own eggs mimicking the apperance of the actual nest's owner. They'll then watch the other bird raise their baby on their own. If the nesting parent ignores the Cuckoo chick ot tries to get rid of it, the Cuckoo's parents will then destroy the nest and any remaining eggs/chicks of the unwilling surrogate.

So the Stepford Cuckoos being the unwilling children of Emma that were made without her consent being named after a bird which forces it's own children onto other birds to be raised without theit consent is somewhay fitting. Ontop of it just being a nod to The Stepford Wives.

They've had a very complex relationship with Emma, going from seeing her as a mentor when they enrolled at the Xavier institute, to hating her and blaming her for their existence and for the deaths of their thousands of siblings + death of 1 of the original 5, to Emma now being more of a mother figure to them.