If you can pull down the coroplast underbelly to access the valves, I would disassemble them (there are 4 bolts that hold the two valve body halves together). Remove the slide bar which will get you access to the rubber valve seat. Remove it, check that it is supple and not damaged. Chances are that if the previous owner didn't care for them properly, they are dry and don't seal well. You can buy replacement seals at most RV dealerships. Inspect the valve bar, if it is smooth, rounded on the end and not damaged, you can reuse it. Inspect the linkage for damage. You indicate that the rods have been bent from forcing them. This would indicate that the cables inside the underbelly are binding. clean and lubricate them if possible and reassemble the valve. Hopefully it will function as designed. If not, or if there is damage to any component, you'll probably need to replace (rather than repair) each valve.
I would probalby just replace the valves and cables if it were my RV, but budget, time and plumbing expertise play into disassembling and rebuilding the system. Many who replace valves report problems with getting everything to line up easily during reassembly. There's little space and virtually no room to work around the valves.
I suppose the first thing to do is to take down the underbelly and see what you're facing. If it looks more challenging than you want to tackle, find a nearby RV dealer to do the job for you. Expect to pay several hundred dollars for the service.