California law is supposed to be gender-neutral in this area, so it could happen. However, as I have explained in other threads (I’ll see if I can find them; I’m not feeling like typing out all the details again):
- the courts have drawn at least some lines against forcing stepparents into parental roles they didn’t mean to sign up for, and
- the law has always preferred exactly 2 parents. So while it’s possible to become a legally presumed mother or father to a kid who already has one of each (or two of one), it’s a higher standard to meet, if you even want it.
ETA: Here’s one thread: Adopting stepchildren: Can children legally have 3 or more parents?