Germany, Austria & Switzerland in 14 Days - Walking Standing

In general, if you want to reduce your walking and standing time you need to consider doing travel "on your own" rather than with a tour. Tours pack as much as the reasonably can into the time they have in a city. When you go on your own you have full control over where you go, what you do, how long you stay and how you get there. Tours are great untill you move out of the middle of the pack by wanting to do more or less than what the tour provides.

The tour states this:

This is a very active tour! Most days are moderate to strenuously paced with 2–8 miles of walking, including hilly terrain and lots of stairs.

So that is the RS tour opinion.

These 3 countries can be visited independently easily enough. English is commonly understood and widely spoken, not by everyone, but by most of the folks you will have contact with. When you travel on your own rather than on a pre-structured tour, YOU are largely in control of how much standing or walking you do. Germany has 5,000+ train stations that make getting around easy. You can buy a month-long Deutschland Ticket (€58) to cover most train trips. Book rooms near the main train station for easy transport as you move between base towns or do outings to other places - and so that you are near a pick-up spot for any city bus tours you might want to take. Take a walking tour through a museum or through an old-town center only if you feel like taking a walking tour.

Both of those tours have the same activity level on the tour pages, so I would expect a similar amount of walking/standing.

I've done 12 RS tours and there is always walking and standing, it's unavoidable.