I see the bedroom is up front near the A-frame. I can only assume the battery box is on the A-frame behind the propane tanks. In this case, I'd run heavy black and red battery cables from the battery, into the storage compartment under the bed and wire in the inverter there. Then distribute AC power from the inverter, up into the cabinets on either side of the bed. Add a battery cut-off switch for the inverter on the battery box.
That all said, I agree with cookie, if you can, order DC adapters for your CPAPs (
here's the cords we got for ours) and run them directly from the 12 volt supply.
Inverters are not 100% efficient and will use more battery than power the CPAPs directly from DC power. If you're running 2 and they have heated humidifiers - they draw a bit of power. In the DC scenario, I'd run heavy black and red battery cables from the battery, into the storage compartment under the bed to a small fused distribution block. Then distribute DC power from the distribution block, up into the cabinets on either side of the bed.