Put yourself in my shoes

Hi ladies I'm in a bit of a pickle. Well my friend is really. See, she is 19 with twins and pregnant with baby #3. She lives with her bf and his family and his sister is ALWAYS starting shit, and the sister has a daughter who mistreats her 1 yr old twins. It's gotten to the point where threats are being made and there is just never piece in the house. I'm considering letting her move in with me and my husband. We have two spare rooms. We have a pug and cat besides that it's just us most of the time.

Would y'all let them move in? It's a big life change and I would hate to have any sort of incidental resentment if things go haywire. Please give your HONEST opinions and any tips that come to mind. Thanks!

I should also mention me and hubby are trying for a baby I'm scared of the house being too full too fast.