I think for FAFSA, you would consider same answer as you’ve provided for federal and state tax returns- regarding how you list your student’s residence during past two years.
Would you fill out CSS Profile for some private colleges? If so, I would think you’d want consistency across Common App, FAFSA, Profile, state and federal tax returns.
Edited to add:
Have you seen MD higher ed website about how to fill out FAFSA?