Having a problem

So my husbands sister is a total dumbass, she has a 5 month old and a d-bag boyfriend with no job (ever in his life and he's 28) and he talks shit about there family all the time! I can't stand it and I hold my tongue a lot! Well she finally came over with the baby, the baby has a flat head and her neck can only turn to the side! I want to sag something but seriously she's oblivious, and her mom is the same way.. My temper is running thin.. What should I do?