Swim bladder disease is really a blanket term, not a specific illness.
It can be genetic, bacterial, or viral (for betta at least...) Obviously genetic would not be the case here.
Bacterial infection, you have a chance of curing. Viral infections are, of course incurable, but symptoms can be managed.
I think you should keep treating with the drug. It sounds like something more serious may be attacking them. Lower the water level for them.
Note that your guys are already getting up there in age, so their systems are already naturally weakened.
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