I know what a hard decision it is for you to get CPS involved but really your sister has left you no other choice. I think your mom tipping her off is a clear sign to you that you and your mom are not alias on this particular issue and it’s probably best not to even discuss it with her.
It’s very hard becoming the sane thinking one among those consumed with the addict. That is why support for yourself is essential.
I think you did something great for those kids!!
((hugs))