I'm 31 weeks ?? About sibiling/Step daughter???

My Boyfriend and I both have children from pervious relationships 2 girls each...he has one bilogical age 10 we don't see much of the 14 year old unless she needs somthing... My girls are 8 and 6 and this baby is due July 20th. Now his daughter he has 50/50 custody but she lives across the street from us and is over all the time anyway and almost every time my girls are gone she's there asking us to take her out to expensive things like chuckie cheese movie anything. She's very clingy to her dad and to be honest he's the only person that shows her love her mom dosnt care about anything but herself and leaves her home alone with her older sister to feed themselves and dosnt get home till 2 am or later...so I get why she's all over dad but she's 10 and still reaches up and saying uppy uppy and has even pushed my 6 year old out of the way to get to him. Might I also add she's a bigger girl and he hardly can,pick her up. She's even tossed herself in the ground when I put her in time out! Her grandmother keeps saying if the new baby is a girl then I'm in for it...I know I'm in for it with both genders because anyone taking away from her is a threat I'm not worried about my children at all but I'm going to need dad after c section to help and im,worried she's going to go crazy and revert even worse and possibly start bed wetting again...She's wasn't at all excited when we told her about the baby and the closer I get to my due date and watching how she is daily I'm worrying myself to death about how we will handle her more then the newborn. Thank you for taking the time to read this and anyone with advice would help greatly.