I would get together with A and discuss the situation. It sounds like you all need to get together on how much you will give C and how you will support her and her baby. If the apartment is lost, C will probably move back in with A? A may need support keeping out C's baby's father from living there too. I think your DH and other male friends might need to do a little work helping in a literal, male-to-male sense, sorting out this man so he either decides he wants to get a job and support his gf and child or move on?

If C can't support herself and baby, can't keep to a giving budget you and A decide on, everyone needs to learn that's the case sooner rather than later. Just giving her money when she decides she wants or needs something isn't going to educate her on being a good mother or even on taking care of herself as everyone must learn to do!