Sorry to hear about the Neons and your Molly.
I bought 9 Neons from Petco about 8 months ago. I lost 1 within a week, ("decor death"... so that was my fault). Then I had a huge Ich outbreak and almost lost a few fish, (the Neons were all I added, so I knew it came from them). Before I knew it, I was down to 6. Now I'm down to 4 because I lost 2 this month, (and they are nowhere to be found!). The Neons are still in my 10g w/ my Betta, so my guess is the Betta ate the 2 that went missing. I also have 1 that has, what looks like, tumors on his lip and body. He still acts fine, but he looks horrible.
Anyway, I've decided that after my last 4 are gone, I'm done w/ Neons. They're pretty, and are active little buggers, but I'm not having much luck w/ them. The Silver Tip Tetras that I added to my 55g a few months are doing great though, (along w/ the Harlequin Rasboras).
IMO though, I think a lot of the fishes that the chain LFS's get are overbred and that's why so many people have problems. It's really hit or miss. I've had good luck w/ centerpiece fishes from Petco, but livebearers and schooling fishes are another story.
I hope you have better luck w/ your next batch of fish!