Total costs less grants and scholarships, and less work study, loans in the student’s name, and any other contribution directly from the student (not the parents).
Regardless of whether the remainder is covered by cash in the bank or the parents’ loans, you are still paying it. If you co-signed a loan, you are responsible and paying it. Basically, anything you pay or must repay.
I believe they calculate the Expected Family Contribution and then divide it among the family members in college. So if you’re already paying at least the EFC that was calculated for sibling last year, I think you can simply divide that in half and expect to pay half for each of the two children.
This means that you must have your financial need for the older sibling recalculated as well.