As with so many things, it depends upon the schools involved. Yes, if your kids’ finances are the same, their EFCs would be half of what it would be if only one were in college. So if your current EFC, is say,$90k,
For one kid in college, which would wipe out any chances of financial aid other than unsubsidized loans, with two in college, each kid would have about half that amount, $45k as his EFC. Which means possibilities of financial aid if the Cost of Attendance for the schools is over that amount.
But, the catch is that no school (with very few exceptions) guaranteed to meet full need as defined by EFC. If your students do go to schools that guarantee to meet full need, it is highly likely that the school uses PROFILE to come up with a Net Price that General be more than the FAFSA EFC. Some schools will not increase aid for students already enrolled, if a sibling Enters college, or will only throw in a small amount more into the aid package, maybe subsidized loans, work study.
The rules about the second sibling’s school can vary too. There are restrictions, conditions, some schools ask for info in financial aid, merit, cost of the sibling’s college, some do not.
You should call the financial aid office of your first student’s college and ask how they handle a sibling entering college. That’s pretty much a fixed entity since you have a kid there already.
You can run the NPCs for the colleges that are under consideration for your second student and consider how they handle sibling’s in college as a factor. For selecting schools.