I have a question (asking for my sister) because she doesn’t have an account and if she did she…

I have a question (asking for my sister) because she doesn’t have an account and if she did she would be embarrassed to ask ok so there was one point in her life where she really really wanted a baby but it wasn’t happening she did sleep with a lot of men not to put her out there but that’s what she did but she still never became pregnant now she has a boyfriend that she’s been with for 5 months and she found out that she’s pregnant today is it possible for her to be pregnant by one of those other guys that she slept with before she got with her boyfriend? Like how long can sperm live inside of you? She thinks that maybe the baby may not be his baby because of her sleeping with those other guys some months before meeting him she had a period every month up until now also.