Breaking Family Rules

I've mentioned this before in my character descriptions on my drawings for the Black Family Tree, but I imagine Marius and Cassiopeia Black stayed in touch even after he had been disowned. I think Cassiopeia broke a lot of rules but never got caught, but it was weird how much she hung out with her brother since he was very critical of her lifestyle (Though I imagine being part of the Black Family you have to deal with a load of unpleasant people)

Also I think Dorea knew that her sister was visiting Marius, and would sometimes ask what he was up to, but didn't have the nerve to see him herself.  

(I have the next part to the Black Family Tree finished, but writing character descriptions is the hard part)    

More of the Black Family: 
The House of Black: Part 2 (read more about my headcannons here) 
Cassiopeia Black
Dorea and Charlus Potter
The Original Black Sisters