Warts On Balloon Mollies?

Hi everyone, I'm new to the site but not new to fish keeping. Just wondering if anyone can help because I can't seem to find the answer to this anywhere!

I have a 64L tank, established for 2 years, containing 1 small angel fish, 1 blind cave fish, 2 small bristlenose catfish and 6 balloon mollies. The temperature is set at 26 degrees C and I do a fortnightly 40% water change.
 
I was given 3 orange balloon mollies from a friend after her fish gave birth. When 2 of them reached 6 moths old, they began to grow lumps all over their bodies that continue to grow and look like warts. The warts are the same colour as their skin. They have been like this for about 6-8 months, with no other issues and the other fish have not been affected. Suddenly this week I've discovered that my black balloon molly (from a different litter) has grown a large wart now too!

A few months ago I tried treating the tank with an anti-fungus and bacterial treatment, which has had no effect.

What could this be? Is there anything I can do to treat it? Is it life threatening to my other fish?
 
Thanks, Laura

Hhhmmm, never seen that before. Can you separate the fish in a different tank? 

Sadly, that's not really an option. I have a 25L tank I could technically set up if need be, but I just don't really have a suitable space for another tank. I guess since they've all been together for so long, the chances are if it's contageous it's probably a little late.

I've never seen this issue before either, and I worked in a pet store for 6 years! I just hope someone might have the answer.

Did you ever find an answer to this? We have a balloon molly who is showing the same symptoms - large bumps on her side.