I am sorry to hear this but it sounds like dropsy to me.
Dropsy is extremely difficult to treat and most fish die from it. The Molly is suffering from.an internal problem (most likely bacterial) and can be caused by numerous things.
What type of feed do you use?
Sent from my Desire HD using...
To answer your questions in short, no the virus ( iridovirus) can not live without a host, so you could add more gouramis if you so choose. Being a operations manager for a wholesale tropical company, they are very few farmers that even raise dwarf gouramis anymore because they can't compete...