The EL2 is battery-dependent, offering just one manual speed should the battery fail. It has autoexposure and is a solid and heavy camera. and performs well. It's like a larger and heavier FE and like the FE the EL2 has a needle in the viewfinder.
The FM requires the battery only for the meter. It's a smaller and lighter-weight camera with very good ergonomics. No autoexposure, and uses LEDs in the viewfinder.
I don't understand why you have to get rid of one of them. I'd keep both.