Orange growth on my molly

That looks like a tumor I cant be exact but it might be lymphocystis--a viral disease with no known cure.
Also 8 mollies in a 15 gallon tank is too many most go with the theory of a 1 inch fish per 1 gallon of water mollies get to be between 3 and 5 inches.
Another note you can rotate the picture by opening it theres 2 arrows under the pic as well as zoom options 1 that goes left 1 that goes right just hit
one of the arrows til the picture is turned upright to desired position. (If you use windows that is)

I should have noted that one molly recently gave birth. I'm getting ready to give a few of the mollies away. Also trying to talk the wife into getting a bigger tank

I also wanted ask what the humane thing is to do in this case. With any other pet with a incurable brain tumor I would think you'd put it down. What do I do with this molly?

Putting him down probably would be the best option possible even though it might be tough to do but leaving any sick fish in a tank you risk possibly getting the other healthy fish sick. Ill post a link for you to read up on humane methods... Hope the wife lets you get a bigger tank maybe she will let you keep the smaller one too for like a hospital or quarantine tank that way you could isolate a sick fish.

https://www.avma.org/KB/Policies/Pa...utm_term=issues-animal_welfare-euthanasia-pdf