Two living together happily, Fobisher Family

[Fobisher]

Hello All:
I have two from babies, M&FM, happily living together, inside and outdoors, GABF. Fobisher Family. The male has never snapped at the FM and they are often on top of each other for days at a time.
Mr. Fobisher is about 9 inches and she is 4. They will only eat mice now, he can eat two large ones at a time, and she only one. I bet he would eat three, but never tried. I keep trying nitecrawlers for something different.
Question, any harm in only feeding mice? Any ideas for any other large live things to feed them? He goes absolutely bezerk if a mouse is around, but she is a dainty eater.
Am I doing them any long term harm, they seem healthy and keep getting bigger.
Thanks