The only way I would go that small would be if that's all you have space for. As already mentioned would probably be okay but only for the smallest of fish.
10 is certainly better, but 5 can work assuming they are around the 1 inch range and for various gobies. If you do start to get larger fish, I would get a 10 gal.
The only issue is water volume and needing to do a water change before the ammonia gets too high.
2 small clowns should be just fine in a 5g to quarantine pending thats all you put in there and keep a very very close eye on ammonia.