you have a range of responses here, and I think the ideas are good: make sure if they have specific conditions that they get medical clearance, individualize for the specific needs of the people who come to you, and so on.
I will mention a couple of things that I have found generally helpful with the group senior classes I teach. Some will need chairs or some other method for balance, so it is good to have them available as needed. It is also good to offer options for those who find getting up and down from the floor difficult. I also think an emphasis on functionality is really helpful. I have some yoga work that is helpful when dealing with bunions that I like to use… a lot of seniors find that helpful. I also like to work on ankle and neck stability and flexibility for my seniors who are still driving. And pelvic floor exercises seem to be really appreciated by many. Particularly with elderly women there are issues of stress incontinence. I also encourage a good bit of light banter and friendly interaction. Their health is as positively impacted by the human interaction as by the exercise.