Marty,
Very few floor jacks will life a coach. You will need to use a bottle jack, preferably one rated at 15 tons or more. The correct location to place the jack is under the axle just below where it attaches to the suspension sub-frame, and of course, safety stands are highly recommended.
The only way to lift an axle to remove a wheel with the average floor jack is to support the coach with the hydraulic leveling jacks and then completely deflate the suspension. This will leave very little weight on the axle and make jacking very easy. However, this can be an unsafe practice, so only use this method if no other option exist and be sure to use jack stands to the frame.
Gerald