Is your tank planted? What are your ph and ammonia/nitrite/nitrate readings? Also do you know why your mollies are dying?
First you need to up your school but instead of neons I suggest getting 6 cardinals as they are better in the long run to keep with angels. Another thing what type of pleco do you have? Compatible fish for angels are Cardinal, Rummynose, Lemon, Diamond, and Congo tetras. Rainbowfish and the smaller Dwarf Neon Rainbowfish and Threadfin Rainbowfish. Harlequin rasboras, Dwarf, Honey, or Pearl Gourami's. Cory Cats, Kuhli or yo-yo loaches. Upside down cats and Ghost cats.. Just research any fish before buying them to see if they are nippy which isn't good for angels and their fins. Many tetras and barbs tend to be nippy so pick carefully. I've listed fish that I personally have kept with angels at one time or another.