When you’re in med school, there will not be “3 in college”. You won’t count because you’ll be in “grad school”. You’ll have your own FAFSA at that point, household size of ONE. Your siblings won’t count you, either.
Doubtful that your parents will be paying for your med school while paying for 2 others. You’ll likely be on your own, likely with loans. If you’re lucky, your parents will help you out here or there.