Black Cousins are all siblings

Alright so, I don't know why or how I got this idea but I kind of need help fleshing it out? My idea originally was to just have them swap parents and write what happens then.

But I have to admit their interactions if they were siblings would be a lot more entertaining, especially considering I was playing around with the idea of Regulus being sorted in Ravenclaw in contrast to Sirius' sorting in Gryffindor and his sisters in Slytherin.

My only issue really, I suppose is like their parents? Because canonically there were a lot of issues with them, and also I just don't really know who to go with for them. So was wondering if anyone had any ideas?