Hello and welcome to Just Answer. I am sorry to hear about the difficulties that you are experiencing in your family situation. There are a lot of issues going on in your life and therefore you have become extremely understandably stressed. As long as you are a loving wife and wonderful mother to your step-daughters and provide for their needs, then their mother should not be so negative. It sounds as though the mother may have jealousy issues with you because you seem to be more well off than she is with her "new" family. Who knows, she may have never completely gotten over the break up with your husband and is out to bad mouth you. Being a step mother when the mother is still in the picture is often awkward. But whatever you continue to do, do not let the mother push your buttons. She wants to feel like she has the power and is in control...even when her daughters are with you. No matter what, do not give in to her negativity. You remain positive. You cannot control what the mother says or does. You can only control your reactions to what she says or does. She will always remain full of bitterness and tries to instill that into her daughters to make them dislike you or have a negative perception of you. No matter what garbage she may feed your step daughters about you, the only thing that you can continue to do is to be yourself and the best step mother that you can be for those young girls who need to have a role model like you in their lives.
Hope I have provided some insight. Thank you and have a great day.