lucky you're stay at home mum, you can take care of your baby. i really cant imagine what will happen if your mother in law is his caregiver, since she didnt take care of her own kids before..
next time your baby cry, just 'snatch' him away from your mother in law, dont let her hav the chance to pass to your sister In law. cos she is YOUR baby, not sister In law, y must she pass to your sister In law insteaed of you?
and i feel that it's very rude for them to come into your room when you're sleeping! esp your father in law! even my own father dont do that!