These hypotheticals aren’t helpful.
FAFSA is primarily used to qualify for federal financial aid (Pell grants, federal work study, direct student loans, etc.). For some families, they might not qualify for as much Pell money as they previously would have. All students who file FAFSA will still qualify for the Federal Direct Student Loans (max of $27K total for most students over the 4 undergrad years)
Most FAFSA only schools (which is most state publics) don’t meet full need anyway, so there’s no guarantee that they would be affordable regardless how they calculate one’s expected financial contribution. Meaning…they often won’t get close to your student’s FAFSA EFC (future SAI).
Your kids will still be able to qualify for merit scholarships, which often have nothing to do with need.
And again, they will have the option to attend a CSS Profile school, where the formulas are not likely to change (meaning if the school currently gives a benefit for multiples in college, they will continue doing so).
Does that make sense?