I am so sorry to hear about the loss of your son and your aunt. Then having to put down Maltese. You have been though a lot.
I almost lost my Kitty this year. He stopped eating and had blood and mucus in his diarrhea. They gave him antibiotics for a week. Then the stopped for a few days and had it again. Gave him more antibiotics for a month. I was still having problems getting him to eat. He was one of those cats would eat anything. I tried so wet foods and finally got something he liked. He wouldn't touch the dry. I finally found one he would eat after trying bags and bags.
He was not getting better. He was so thin. Mind, he had blood work, nothing. And we did X-rays and sonogram. Still nothing. He started throwing up the antibiotics. I stopped them. I finally started to look holistically. A Biewer breeder recommended Vitality Science. She told me to talk to Steve. I have to say I am giving him three different items and it is working well. He gained some weight and wants to eat. Maybe talk to a holistic vet or take him to a specialist. Sometimes even your best vet can't figure it out.
https://www.vitalityscience.com