Is there any way you can schedule on a day that BIL is out of town?

It's your wedding. Elope if you want; however, it sounded like you wanted your parents there. Go with parents only if all involved can keep the wedding a secret. If you suspect someone can't keep his/her mouth shut, then make it a parents get together event with your wedding a pleasant surprise. You will find yourself saving a lot of money and headache.

My cousin did this. To be honest, some of the family was annoyed, but it's not like anyone held a grudge. They invited parents + grandparents (they each had one living grandmother). Courthouse ceremony, nice meal afterwards.