Exercises can definitely vary depending upon the individual and how progressive their osteoarthritis is. A lot of times taking them off weight bearing and just having them go through different movements through their joints will at least warm the body up and increase circulation. Also if you have a warm room to work with them in, that can help as well.
I get the best results when I work with these types of clients by focusing on their nutrition. Take out foods that may be inflammatory. Add in collagen and/or bone broths. Big one is to take our processed sugars. A lot of times this alone will make them start feeling better within the first week or 2!