How is a fires net supposed to used? should CCA and CAS be on fires net or Command net?

Eitherway the fires net should always be active sending frontline traces establishing targets giving left and right limits and communicating with all the other FO's in other platoons to ensure everyone is tracking what you see and where all friendlys are and if your at a OP setting up TRP's so the FSO and FSNCO can battle track and you know where all your guns are at all times to ensure they can range the targets because these are things the commander needs to be tracking

Situation depending, how active is the fires net? Are you conducting a JAAT? For me all separate nets unless doing a JAAT, then all the same net just for TOT or TTT of mass fires.

Cas is for your jtac they should have their own freq at cmd or jtac operatior, so the answer is command unless otherwise ordered