I really wish I could be more help in the coming days, but it is really difficult to know what to do when we don't know what is wrong with them.
There are other things that could cause the fluid. Whether it is likely to be calicivirus or distemper, I do not know. While I was trying to find some information about your situation, I found a number of things that COULD cause fluid buildup, but nothing definite.
I believe Calicivirus can be treated, as can bacterial pertonitis (I am still unsure of what causes this...as I said in an earlier post, I could not find much information about it. But, I do recall coming up with various bacteria/parasites.). Distemper is more difficult to treat - that said, I'm not too familiar with distemper, but what I know about it doesn't really match your situation. I could be wrong though. Those are just a couple of options.
Here is a post from the Yahoo! group about some of the differential diagnoses. Warning, it is a little bit overwhelming, but I think you can eliminate all possibilities that are not infectious/contagious, and that are slower progressing.
FIP should be considered in the differential diagnosis of any condition that causes peritoneal or thoracic fluid accumulation and in any chronic wasting disease of cats. Effusive FIP with peritoneal involvement should be differentiated from ascites due to congestive heart failure or hypoproteinemia (renal and liver disease, glomerulonephritis, malabsorption, parasitism), neoplasia, bacterial peritonitis, pansteatitis, toxoplasmosis, tuberculosis, pregnancy, and trauma. Differential diagnoses of effusive FIP with pleural effusion include cardiac insufficiency, neoplasia (lymphoma), pyothorax, chylothorax, cryptococcosis, lung lobe torsion, diaphragmatic hernia, and trauma (hemothorax). Differential diagnosis of noneffusive FIP includes neoplasia and other systemic infectious diseases such as toxoplasmosis, nocardiosis, actinomycosis, tuberculosis, and deep mycotic disease (cryptococcosis, coccidioidomycosis, histoplasmosis, blastomycosis).
Please be aware that this list may be longer, I would for example add IBD, Feline Panleukopenia, mycoplasma infections, chronic URI, stomatitis, tick borne diseases, FIV, FelV. Much depends also on how knowledgeable your vet is on FIP and other feline diseases.
The one thing that I would be interested in seeing from your tested kitty would be if his/her liver is functioning properly. During my research, that organ came up often and does seem to be a POSSIBLE culprit for fluid accumulation.
Unfortunately, short of an emergency vet, I'm not sure what you can do to help your kitties until you can get one of them in for blood work. Keep them comfortable and try to get some fluids and food into them (you may have to force feed/syringe water them).
I really hope everyone makes it through to Friday and maybe then you will have some more answers.