If a student attends a public FAFSA only school… like umass or uconn… you can fill out the FAFSA stating that an older sibling is in grad school. FAFSA counts grad school as 2 in school …providing that the grad student has a certain % of parent financial support (50%?). This can be clothing, transportation etc.
However… this won’t matter… at all… on any level… for schools that do not meet full financial need. A school such as Penn State, Ohio State, UConn etc… will not care about your FAFSA EFC being lowered because of grad school. It will only matter IF a school DOES meet full financial need… and … IF the school counts grad school as 2 in college ( most do not, but some do).