Make sure you speak with an attorney for legal advice. Most likely as long as you have a will in place and it is well prepared so there would be no problem. Since the father has not been in the picture, I do not believe the family courts would even consider the paternal rights of the father. Although, you never know. More than likely the family courts would automatically place your child with the most suitable interest of the child in mind. if your child has an established bond wth either sister or mom they would be looked at first.
However, if your child as a bond (meaning lived with for an extended period of time) like a boyfriend as a dad figure he may in some states have rights too.
If, your intent is to just make sure Dad can't get child when you pass, you need to prepare all of that now. Depending on the current status of their relationship will make a difference as will the status of mom or sister's relationship. They will need to pass home study, etc.
Sorry, this is horrible news. May God bless and keep you and yours in his arms.