A few suggestions please:
-Paris: They could consider including-
- Louvre
- Palace of Versailles- a little far but connected with metro and then a cab/ bus.
- See the Eiffel Tower lit up at night (used to be at 8PM every night for 5 mins, earlier. Now i believe they are doing it from sundown- which itself is quite late in Paris)
- Disney Land both parks are primarily for kids, even teenagers. Maybe even you at your age and the lady could enjoy a few rides. But how many rides would the Parents be able to take at their age, needs to be looked into before you buy the ticket.
-Switzerland:
- If visiting Mt Titlis from Zurich/ Lucerne, Could consider skipping Mt Diavolezza. Both are similar experiences with the train and a long cable car journey and like destinations.
- Time and budget permitting, include a trip on the glacier express, since they are already going to St Moritz. Its truly breathtaking.
-Italy:
After the mandatory Gondola ride, Venice is best explored on foot through its hundreds of narrow bylanes, teeming with tourists. Its quite a walk so they must plan to start early evening and with some breaks in between. A dinner in any one of the cafes lining Rialto Bridge really helps absorb the ambience and is recommended.
- Florence: Academia and Uffizi Galleries are both must see. Both are ticketed so if its a hard choice between the two, then see Uffizi first and then see the 'first copy' of the stunning sculpture 'David' by Michelangelo which is otherwise in Academia Gallery, at Duomo Square, just opposite the Palazzo Vecchio for free!
- Pisa is easiest to reach from Florence. well connected by train.
-Rome:
- Must include Colossium and Roman forum (same ticket) and Pantheon.
- Trevi Fountain close to Pantheon is also worth a visit.
A general suggestion applicable at all attractions in Europe. They must always buy 'Skip the Line' ticket. The lines of tourists to gain entry at any place are insanely long. They'll save themselves a lot of hassles and of course time. It is a few more Euros well spent.
Regards.