BMs half brother (she didn't really have a relationship with him) died recently. From the obituary, along with some background info I already knew, I gathered this:

GBM got married, had a few kids, got divorced and left kids with dad. Got remarried and had another kid, divorced again and left that kid with dad. Remarried a third time (to BMs dad), had 2 more kids. Got divorced again, left the kids with dad and moved in with the man she's still with today. 

GBM is just like MIL in that she loves to be a backseat driver grandparent and meddle and tell the parents to parent in ways that they themselves did not. I know she also likes to stay involved in BMs dads business and keep some control there, so I would imagine it's the same with the other exes also.

Guess that's where BMs idea that having a kid with someone meant she got to control them and have them be her b*tch forever came from.