Now that you’re down to 3 it becomes easier to start laying out head to head comparisons.
One of the other things he can do is lay out and compare the requirements for his major at each school. Some may have different “core” requirements, some might have different options for concentrations, or minors, etc.
Send a message to the department chair, how many students in are currently in the program? Do they have any statistics they can share on outcomes. Based on his major, how easy is it to do research? Do they have any partnerships with zoos? or do they sponsor research trips over break? Do any of their professors current research line up with your sons interest.
Lay out all the other stuff, total cost, campus vibe, etc.
Lastly, don’t rush to commit, it’s very tempting for HS kids to want to just move on, but nows the time when he has the leverage.