Hello Richa, Italy is an extremely difficult place for people who do not walk well. Keeping in mind the age factor, I will suggest you to include only 2-3 places like Verona, Venice and Ravenna. These 3 places are located close to each other, hence your aunt and her friends will not face difficulties in commuting. The best time to travel to Italy is from April to May and September to October when the weather is extremely pleasant. Check some good staycations for them here: https://www.tripoto.com/hotels. I will suggest you to book a complete holiday package for them from a verified tour operator.
3)Try watching a football game at San Siro Rome
2)Saint Peters Basilica
6)Museums of Vatican Florence
4)Try planning a day trip to Pisa and Tuscany of possible. Venice
4)Saint Marks Basilica
6)Island tour to Murano,Burano and Torcello