I would put a note in the BS FA application next to your sib’s college costs noting it will be his first year and he does not yet have decisions and FA awards in hand. You may want to put the higher cost # for him and tell the BS you’ll need less if he gets scholarships . AND you should follow up with exact costs when you have them.
It’s always a challenge to weigh every kid’s needs and wants within a family, and it is possible that someone will have to compromise, so you should be thinking about how to manage that as well.