My thoughts are with you & your family. It is such a hard decision and I pray it is not one you are forced to make.
May the treatment work or the allergy tests show that he is not allergic to the kitties.
I understand completely about your mom taking custody of Payton. After all it is her cat. Like you said he's going to a great home & you will get to see him often.

I have bouts of eczema once in a while & never knew that it could even be allergy related. My Dr. has never once said anything about allergies & he knows how many pets I have.

HUGS