I thought of one other way to possibly speed up recovery. If you can get some sterile saline solution and give the snakes a daily subcutaneous injection, it might help them towards getting rehydrated. No different from getting IV fluids when you are sick. Any Vet should be able to tell you how much fluid is safe to inject. I have given SC fluids to my boas when they had respiratory infections and I was treating them with amykacin. It is simple to make these injections and might just kick them back on the road to recovery.
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Rick Staub