First of all, remember that all of your interior lights operate on your 12-VDC electric system which is powered by your COACH batteries.
So, If this RV is new to you I would suggest that you replace the old batteries with brand new deep discharge batteries so that you will then be confident in them for the next few years.
And if this doesn't fix your light problem then next you should check the 12-VDC FUSE Box, for a blown fuse. This fuse box is not the same as the 12-Volt system under the hood which is for the engine. It can be located anywhere in the interior of the RV, under the dash, along the wall in a closet, anywhere. It should use automotive fuses.
If all of these things are OK, then get a multimeter and check the voltage across the battery terminals. It should be around 13.5-VDC (charged) to 14,5-VDC(charging). Any reading below this means your Converter is not charging the batteries.
One of these actions should find your problem because all of the lights are factory wired and should not be broken.