Depands on the dynamics of the church.....
1.if Keys 1 is an organ...
keys 2 can be piano, rhodes, strings brass....
2. if Keys 1 is a piano..
keys two can be strings, brass, organ
But keys two should be subject to keys 1 who may be the chief musician......
HOWEVER...
Ultimatly you gotta play your position....
I was chief musician at a chuch once (keys/synths),but when i felt that I wanted 2nd keys to stretch out, i'd tell him to take lead.
Ask the main musician what is your supporting role. (always get an understanding)
Usually, its to add sweetening to whatever 1st Keys is doing. depends on the song. In my church, 1st keys plays a Yamaha P250 (grand piano), I have a rig with a triton, Motif 6, and a Korg CX3(hammond-type) I like having differnt flavors available to me. Im usually strings, synths, brass, but sometimes hell be like, "take piano on this"
hope that helps.
Wolf