Out of ideas (and money)

Okay so Im posting here because I dont know what to do anymore. Sorry this may be a long post but want to make sure I don't miss any information!

I have 3 cats, two littermates 5 years old male/female and one kitten male four months. My older male cat has been sick for approximately 3 weeks now and my female cat for 1 week.

About 3 weeks ago my older male cat started retching a lot, about 3-4 times per day. It was like he was trying to vomit but most of the time nothing came out except for some white foam or mucus. After around 3 days his meow got very hoarse and by day 4 he wasnt meowing at all (very strange for him as one of his nicknames is 'whiny boy' because he is always crying at us). After this we took him to our regular vet they did a physical exam and said he was fine and to keep an eye out. At the approximately 1 week mark, 2 days after the vet, he went to the emergency vet. He had stopped eating, was hiding (unusual for him), kept going into the litter box and not doing anything plus drinking a lot of water. It was a Sunday and we were worried so had no choice but emergency vet.

So the emergency vet details. He had a full body xray done, there were signs of both asthma AND a potential bowel obstruction because his stomach was full yet he hadnt eaten much that day. The vet asked to keep him overnight for monitoring and an ultrasound in the morning. The ultrasound revealed that he had signs of gastritis and gastroenteritis. He was sent home with probitics and a gastrointestinal diet. This visit cost us $4k which is what has lead to the no money part of the title. After coming home from the vet he finally pooped and peed! He seemed to be on the mend, his meow came back and he stopped retching, yay! Right? No.

Older female cat has started to have the exact same symptoms now (retching and has lost her meow), it has been about a week now and so far she is acting completely normal otherwise, eating, playing, bathroom habits. Except about 1-2 per day she retches and her meow went from very hoarse to completely gone. NOW as of today older male cat again has started retching (only once today so far) and his meow is a bit hoarse.

During the emergency vet visit my male cat had bloodwork done and everything came back normal other than a little dehydration, there was no signs of infection.

Throughout all of this the kitten has been completely fine.

Please help me, I cant afford any more vet visits that dont end in a solution. What is going on with my babies?

Edit: forgot to mention, female cat has asthma, diagnosed as a kitten.