You poor thing its the one part of having a teenager I'm not looking forward to. Can you kinda nurture the relationship - have her around and maybe even try to talk to her about these things because it sounds like she doesn't have the best role model for that in her Mum? At least that way she is in your home and you can keep a watch over what goes on, otherwise you know they will just sneak behind you back and do it which is far worse. If they are at your place you can have a little control over things kwim? And maybe explain to your boy that you wont support a pg teen girlfriend at this age and ask him all the things like how will he pay for a baby etc. Poor kid is probably totally smitten by her and isn't going to be open to anything like that and will more than likely take everything you say as a criticism of her and get defensive but you can at least try. Good luck