Without knowing who said what when the tires were ordered, it is difficult to say who is responsible for the wrong tires being installed on your coach. The facts are that your coach came with 11R22.5 load range H (16 ply rating) tires that were minimal for the weight of the coach. The G rated tires that you have are rated at 435 pounds less per tire than the H rated tires that the coach came with.
In my opinion the tire dealer and the RV dealer are both liable, but I am a retired mechanic and not a lawyer. If you make a little noise Monday about the legal liability of installing underrated (unsafe) tires on your coach, the RV dealer will probably seek a solution to your problem whether he has any liability under Florida law or not. However it would be best if you knew how much your coach weighed, so you would know how much the tires are overloaded. You may have to pay the difference between the 11R22.5 and the 295/80/22.5 tires, but that will be minimal. However remember that they are your tires and you have to make sure that you are safe.
With the G rated tires that you have, your front axle will only carry 12350 pounds. I think that all of the 2000 Marquis coach front axles were rated at 13200 pounds, which is all that the 11R22.5 H rated tires will carry. The 14600 pound front axle rating that you stated earlier would require at least a 12R22.5 tire that was not installed on Marquis coaches until 2002 to the best of my memory.
Gerald