Anyone have any tips for those with Rheumatoid arthritis?

No, but I'd like to know as I have a client who has it. I've heard that with osteoarthritis the best thing is to move.

My experience and training with clients with RA it is quite different from OA. The pain from weight-baring (elbows, knees, wrists) fluctuates depending on whether the client is having a 'flare-up'. Their r.o.m is often limited and their balance is often compromised because of ankle pain. My advice would be to ask the client at every class how they are feeling and modify all exercises that aggravate the condition.

I'm an instructor, and I have RA. For me, the joints in the hands are the main ones affected, but it can be different for different people. I think that the key thing to know is that mechanical stress on a joint can cause a flare up, which can be quite painful and take many days to settle back down. For folks where the hands are affected, it's good to avoid full wrist extension (for example, for planks you could have the hands on the sides of the bench, or on a half roller) and avoid lots of gripping (for example, for someone having a flare up you might want to skip hands in straps exercises). People may be able to do different things on different days, so just be guided by their comfort level. People can often feel worse in humid weather.

Thank you for your feedback. I found I was asking how she was doing during the session, and the following days!
So this was good to know about the flare ups, humid weather etc...

Wouldn't foot work on and off the reformer be very valuable for these clients?