Without knowing your rig I would guess the following;
Antenna above the passenger side goes to the stereo in the overhead cabinet. The antenna above the drivers side goes to the in dash radio, the whip antenna mounted to the drivers side wall near the top goes to the CB.
Pictures would help.
1999 Newmar Mountain Aire MADP 4080, Cummins ISC 8.3L, Allison, Spartan MM IFS, Howard Power Center, Chev Trailblazer LTZ Towed w/ BlueOx rigging, Segway X2.