Rehearsal dinner date

I know the rehearsal dinner is normally the night before the wedding. However, my baby brother is graduating from marine boot camp 09-17-2021 and my wedding is set for 09-18-2021. My Future Husband and I discussed moving it up to 09-16-2021 but found out that’s the “family day” at Paris Island. The other issue is my nephews birthday is 09-15. So now it’s looking like I’m going to have to push to either the weekend before or the beginning of the week to attempt to be able to fit a rehearsal dinner in. My nephew agreed to let me “borrow his birthday” as he called it (he’s 9, gotta love him lol) if he could have a birthday cake for him there. I just feel bad for taking over his birthday party with wedding stuff. Should I just try to make it the weekend before? Or use his birthday since we all would have to get together anyways? We had originally planned to go to the venue and do a run through and go to a separate restaurant afterwards.