Can a prenup cover child custody if my marriage doesn’t work?

After 5 years of dating and having a child together, my boyfriend and I are engaged. I have a lot more assets than he does and he has a large student loan. I want to get a prenup to protect what I have and to not be responsible for his debt. What do I need to do to get a prenup and can the same lawyer represent both of us to save on legal fees? Also, a few times during our relationship he’s threatened to take our son from me if we ever split up. I work a lot and he’s been the primary caregiver. I want to make sure that if we did end up getting a divorce, I have at least equal time with my son. Can we include that in a prenup now? Would a court consider that I have to work to support us if we did end up fighting over custody?