Well - he really is still in the right place at the moment then isn't he? It's not just a matter of having X amount of any random make of insulin daily and that's that I'm afraid. He could have come down with something else in the meantime cos sorry, but hospitals are breeding grounds for bacteria and the staff know that for the simple reason there are more sick people in them in one concentrated area than anywhere else. Husband's been in hospital this week for a planned operation and told the team he was more worried about what he might catch in there than he was of the operation - which was 100% truthful cos when you have COPD and in your 70s it gets tricky when you get a chest infection. Anyway point is if you get anything even a flipping cold when you have diabetes - it elevates the BG!
So - it could be that or - it could be summat else eg needs bigger dose(s) of insulin or a different sort of insulin. It's really quite complicated but an EXCELLENT book for people like you two (and probably his grandparents depending how involved with him they are) is by Ragnar Hanas - Type 1 Diabetes in Babies Children & Young Adults - about £25 ish from Amazon, make sure you get the latest revision which I think is 2022.
And good luck to you and him, you WILL get there!