"I have been told that I have 3 different wheels on my 37 foot"
All wheels should be interchangeable on the same vehicle. You might have 3 different finishes, if you have Alloy Wheel, Polished on the Convex side for the Front, Polished on the Concave side for the outside rear dual and a steel wheel for the inner duals.
Except for cosmetic purposes, they can be used in any position, except for putting two alloy/aluminum wheels on the same rear corner. The alloy wheel hub/centres are much thicker than the steel hub centres, the studs may not be long enough.
If you have steel wheels and wheel covers, most likely all your wheels are the same.
Tires, just check the front and rear tires for the sizes on them, The rears all have to be the same, in some instances, the fronts may be a different size, but all tires on the same axle should be the same size.
Beverley and Ken