Normally you’d want a client to stay away from machines and keep them on barbells/dumbells to maximize the bang for your buck.
However, with seniors you have to take into account limitaitons in bone density, muscle strength and balance.
Keep them on machines that mimic compound lifts- presses will be their friend. Leg press, chest press, shoulder press, etc.
If they can stand, get them to do squats with a chair.