They still sleep with their mom in bed, the oldest has started pulling her eyelashes and eyebrows out, and she takes a caretaker role at her mom's who is always "sick".
Are the girls getting any therapy? If changing custody isn't an option, is there any way you can order a psychiatric evaluation, especially for the child who is pulling out her eyelashes?
They sound very parentified, which is common for kids with BPD moms. Without therapy, their psychological and emotional development is going to be stunted
Validation will go a long way to giving them something they probably don't get from their mom.
Panda's suggestion for Power of Validation is excellent. I would add the Lundstrom's "I Don't Have to Make Everything All Better." There's an important chapter on asking validating questions that will help the girls learn to identify themselves as accountable. This is a building block for independence.
And if you are concerned about the girls developing BPD, BPD in Adolescence by Blaise Aguirre is excellent. It's not certain that the girls will develop BPD but you want to have some understanding of what to look for as early warning signs.
What kinds of things do the girls say about their mom when they are with you? How is your relationship with them? Maybe we can help brainstorm some ways to respond when they talk about stuff with you.