For the ‘two kids in college get a benefit’ this was a small group of students under the old system to qualify for a Pell grant. The EFC on the first student had to be between about $7k and $14k to qualify for a Pell if cut in half. (those with EFCs between $0-$7k would benefit by getting double the Pell , which is a good thing too but not enough to fund a year in college).
Say the EFC was $10k for one kid (not Pell qualified), if a sibling started school then both students would get a partial Pell (about $2k each). If the EFC went up to $20k, then having a sibling start school would cut the EFC to $10k, and again, not Pell eligible.
Yes, some schools would look at that $10k EFC and award some need based aid from the institution that they might not with a $20k SAI, but they can award their own money under the new system based on a higher SAI and ask if certain conditions are present - siblings in college, special circumstances- it’s the school’s money so it can set the terms for awarding it, using the SAI or another system.