I've taken the tour. Everything is optional.
Salzberg - walking, all level or slight incline.
Zugspitz - stop only if weather permits, lift to top, no hiking.
Dolomites - lifts to the top. Your choice of how much and how challenging. One woman did no hiking at all on the tour (hip or knee problem) and still had a great time that day.
Fussen - if you go to the castles, there's a lot of up/down hill to get to the castles and lots of stairs inside. There's easy hiking around the lake. Or stay in Fussen, pleasant little town, and walk around. It's flat too.
Lauterbrnnen - easy hiking in the valley. Lifts up to Gimmelwald and Murren for easy hiking in the villages. My tour had literally no visibility from the peaks, so none of us took the lifts to the top.
Chamonix - mostly flat in town, lifts to Aiguille du Midi for viewing. No walking, but there's a flight of stairs or two. Seeing the glacier (not much IMHO) and walking through the ice tunnel requires a LOT of stairs down and then back up. The woman who did no hiking went paragliding!
The tour leader used the bus time to tell us what the activities were for each approaching stop. Then she went through the group and helped everybody individually to plan their day. My tourmates were a very diversified group. A couple with 3 kids, ages 9-11, 2 college kids, experienced hikers in their 40's and 50's, and some older folks with varying hiking experience. At every new place, the guide took us on an orientation walk. She organized about 3 happy hours, but the group kind of gravitated to the hotel bars every day for happy hour, after the first one.