My H does the same type of stuff to deter me from going to therapy. The worst is when someone like that sucks all of your energy dry right before you go to your session. This happened to me last week and I didn't talk about anything I wanted to talk about.

The only way I've been able to deal with these attacks is to avoid discussing therapy with him. I don't lie, he knows I go, but basically that is all. It is not a good solution (certainly doesn't help with our communication problems) but it is the only way I can defend myself from his attacks at this point. If your mom in anything like my H, she will use any information you provide to further undermine your therapy or discredit your T.

As for your sisters, I guess it depends on how old they are and why you are talking to them about your therapy. My childhood friend tried repeatedly to talk with me about our shared abuse. I was not ready to go there and cut her off. This created a lot of tension between us for many years and increased my guilt and shame when I finally decided to revisit the past. I think you can be supportive, but don't push discussions about abuse. Maybe they just need to find their own way to healing. Maybe just letting them know where you found help is enough at this point.