Just looked at OP’s other thread, not sure what is different now.
Is the $20K gap still the situation? If so, you son can probably make $5K this summer in a job (more if he starts working right now). He can take the $5.5K first year student loan (it is ok for him to graduate with $27K in debt IMO unless more school is in the future), and work during the school year and make say another $2K. So, the gap is now around $8K. I doubt the school will pony up more merit than the $25K he has already received. You can ask to be sure. Is filling an $8K gap possible?
Since he has a full ride at another school, I would seriously consider that.