How can I best deal with my toxic (future) in-laws?

I have been struggling lately with how I feel about my fiancé's parents and how I don't really want a relationship with either of them.

His dad is a bully who has no respect for anyone, but demands it out of others. He jumps at every opportunity to attack others and belittle them, including his children (and me). He doesn't respect anyone's opinion if they differ from his own and basically feels his children owe him their lives just because he raised them (he doesn't do anything else for them now and hasn't since they've moved out).

His mom is extremely selfish. Nothing she does is out of the goodness in her heart, it feels like she's just waiting to cash in if she does anything. She's going through a breakup right now and it's stressed us out to no end because she blows everything out of proportion and has unnecessarily involved all of her adult children in the chaos. She can't properly deal with her finances and can barely afford any of her bills. Her boyfriend (that is breaking up with her due to constantly being made to feel guilty about everything and continuously accused of cheating. Did I mention she cheated on my fiancé's dad twice during their marriage?) was paying for the mortgage on the house and HER car insurance among other things. For four years, she's only been paying for groceries and cable though we are fairly certain she makes enough to live on and had a substantial payout from the divorce. I fear when she has to move out on her own, she won't be able to manage and she'll get evicted... And then we will have to take care of her since my fiancé is the eldest and we are the most financially stable. I also fear it's driving a wedge between my fiancé and I since I'm losing respect and empathy for her since she just continues to do stuff like this.

Any advice on how to deal with toxic people you more or less have to be in contact with would be helpful... Feel free to also tell me I'm being a jerk if that's the case. I just hate this whole situation!
How can I best deal with my toxic (future) in-laws?
Post Opinion