I have to assume that these people don’t have medical conditions. If they do then you need to stop and address these concerns and conditions first.
So, if they just haven’t moved they probably don’t like to move. You need to make things easy and enjoyable. You will need to be the sunshine. Keep it simple, walking, stepping up and down, using a chair to stand up from and sit back on. Watch the sit and be fit videos.
The most important thing is to do things they like to do… play music they like, if they like being in a pool and have access get them in the pool. The goal is really simple get them to move without them being sore the next day. They need to “enjoy” movement. I find that people who don’t like to move or haven’t moved much need a lot of “mental” coaching.