You need to check the college policies. They vary.
- Having a sibling in college will affect your FAFSA EFC... u there is NO guarantee it will impact the actual,aid you receive. Most colleges do not meet full need...so your aid might not change a dime when there are two on college at the same time.
- In terms of counting a grad school sibling....you will have to check with each college. Some will...and some won't count that sibling when computing your need based aid. Most don't.