Just tell Rush's vet what you posted here several posts ago - the one that starts "I'll ask about a different kind of insulin" (post numbers don't appear while typing a new one!). Even print it out. You are best to get some suggestions from her.

If you family can't put the money into getting Rush checked out - a drastic option is to surrender Rush to a rescue and letting them look after the medical. You would have to pay to adopt Rush back, if you were allowed to at all.

Good luck.