I hope that you get enough time to bring all of this up with your psychologist DM as I am sure it would really help if he/her was given the full picture including all the background info.
Tell me if I am speaking out of turn here but it seems to me that you have enough on your plate without having to be responsible for your nieces who are ultimately someone else's children. I don't mean it in a horrible way - it just seems unfair on you and your husband
Maybe you could assert yourself in that area of your life at least
I wish you all the best for tomorrow - it can be a good idea to physically write down on paper all the things you want to say - nothing worse than coming out of something like that thinking "why didn't I mention....."