Negative or toxic people can be strangers, friends and even family I guess; History is full of examples of that and I'd say your situation is not altogether isolated. I do not believe that one should, or must, keep a toxic person around due to the fact they are family; It's not a good enough reason to do so in my opinion. It's good learn from them though, what not to do, and I think that's the best thing to come from negative people.
I hope you're well, and will have some time for a break over the weekend.