Reminds me of a French film where the parents got divorced, then they each remarried, had kids, divorced their respective spouses. Then the spouses from the second marriage got married to each other, among other complications.
Long story short, it's a really big, blended family with, like, eight kids who keep changing apartments every two or three weeks, due to shared custody agreements. Then, the oldest kid has the brilliant idea of moving the kids into Grandma's apartment while she's on holiday, and the adults can take turns visiting.