When it comes to osteoarthritis, whenever you are trying something new, you may experience a little discomfort. A good rule of thumb that I like to use is anything above a 5/10 (0-10 pain scale of 0 meaning no pain, 10 meaning the worst pain you've ever experienced) is usually your joint telling you it's maybe had enough of that exercise and will require a modification. If you experience pain less than a 5/10, odds are your joint will be okay with it.
It is important to pay attention to recovery as well. If you experience pain and/or swelling after activity, take it as a sign from your joint that you may have done too much. In this case, the next exercise class you will want to modify some activities and take breaks as you need to. You are asked to use your judgement and can ask any further questions in the support group discussion!