The idea is fine. The execution is terrible. It’s sort of a queuing problem. He needs to schedule like they do in the military, PLAN AHEAD OF TIME and OVERSCHEDULE to offset weather cancels, instructor and aircraft availability issues, etc.
He needs to schedule to task, NOT just look to the next lesson. But whether he will except that advice coming from you - that I don’t know. All you can do is to tell him that if he doesn’t do this EFFICIENTLY, he’s losing substantial time which assuming he does someday fly wide body for a major may be as much as $40K a MONTH at retirement. He’s also burning you out and imperiling the family finances.
If he needs to go to a bigger school with more aircraft and instructors and better sche$uling availability, he needs to do it. Get that commercial license and then GET A JOB. And until he does, even working nights at McDonalds would help.