Advice on watching another child with my newborn

My niece will be just a little over a yr when i have my first baby in the next month or so. I watch her 5 nights a week so her mom can work (both parents work nights, desperate for money). This child has never had a sleep schedule, and she only co-sleeps (which includes waking up every 2-3 hours and random 20-30 minute moaning and rubbing our arms and stomachs as a comfort thing). If we put her in a crib or play pen she is up screaming within 30 minutes every attempt. And crying it out isnt an option in our thin wall apartment. She doesn’t usually fall asleep until 1am every night. She has been raised on WWE and south park and has no interest in childrens shows or books. I know my sis-in law needs this job, and im one of the only people she trusts/has available to watch her child (personally i dont see anything wrong with grandma watching her). I know i cannot handle trying to be a brand new breastfeeding mom, who runs not only on a newborns feeding and sleeping schedule but a one year old’s sporadic schedule. Two kids two different schedules. And it will be hard for me to enforce a sleep schedule with my baby when the other one stays up and wakes up my child. If i tell my sis i cant watch her child she will end up not having a job, but she will not enforce a schedule for my niece no matter what, and im sorry but my husband works nights and has two nights home and both those nights we have a 1yr old between us, we dont have any romantic time or cuddling or anything then because of it. This child is interrupting my closeness with my hubby when he is home due to how she was raised at home. What do i do??? I only have a little over a month before my baby is here and i feel like im going crazy. via /r/Parenting http://ift.tt/2lDiUyc