What was the EFC for just one in college? Divide that by 3 and if that number is below $6000 they will all get some Pell grant, probably some SEOG (it really matters when they file as most schools award that to early filers). Make yourself well known to the financial aid office if they are all going to the same school.
At orientation for my daughter, I met a really nice kid who was trying to talk her into ROTC (not a chance!). I learned was that he was one of seven kids, and his parents told them they’d pay for one year of school but then the kids were on their own. It helped that Wyoming is very inexpensive for instate tuition and R&B, about 14k per year if one is full pay, but hardly anyone is full pay. There are state grants and scholarships for almost everyone instate. He and some siblings had ROTC scholarships, some siblings were RAs so got full room and board as upperclassmen. They all worked, borrowed books, lived ‘small.’ It takes some sacrifice on the part of the students too.