Hi, Shivangi!
May is a great time to enjoy a vacation with family. However, if your mother has a knee condition, the most suitable places can be Nainital, Shimla, Munnar, Manali, Mussoorie, McLeod Ganj, and Dharamshala. These are some hill stations which have pleasant weather during May and also don't demand too much walking. However, it's recommended that you check with your accommodation about the transport and other facilities which makes it easier for you and your mother in that particular destination.
Tiger tracking expeditions are worth it from October to July. The rides are in comfortable gypsies and the stay is luxurious. Let us know your dates and we will book the best packages for you . Visit www.firale.com for the best wildlife tourism packages.