I've met family members who were into bdsm and went to events together. I went to a play party with an older sis. She did her thing. I did mines. No overlap. In the context above...
We can view their kink as very progressive and ahead of its time. Or conversely it can be viewed as an abhorrent. However if they all live in the same household and all.pay towards the bills together the finances can be viewed as fungible. And they would be spent roughly the same regardless of circumstances.