JMHO. I would not buy tires till your ready to move the RV, if they are holding air.
You want tires that are rated for trailer use of the same or higher load rating than what came original equipment on the trailer.
When jacking up my 5ers, I always placed the jack under the spring mount plate, floor or bottle jack, anywhere else on the axle you run the risk of bending the axle and throwing the alignment out.
If you want to take all the wheels off at once , to go for replacements , support the trailer frame as close to the spring mounts as possible, that's the place designed to carry the weight.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.