There are instances when the mom just can’t distinguish who is the father of the child she is bearing. It often leads to confusion and ever fears that none of the suspected fathers would claim it. To clear things out, the mother can do at home paternity tests by simply counting the days of gestation against the day the intercourse happened.
If it’s really impossible, then better wait for the baby to be delivered and have a DNA test. This may cost you money but you’re doing your child a huge favor and that is giving him or her the chance to know his/her biological father.