As always with training a client with medical issues make sure you are in communication their medical doctors and have do’s and don’t for this client.
I do balance work with all of my clients and find it essential.
I always make sure the area is clear of possible hazards and I always stand next to my client in case they need to “hold on”. I suggest that they immediately stop the balance work if they feel as if they are going to fall.
With MS it depends on the severity and restrictions. Starting balance work while seated would be a good way to introduce picking one foot up off the ground. Once they feel comfortable with this the next move would be to do it while standing and holding on and progress from there
Balance work can and is frustrating for many people. Remember to encourage and know when to back off if they are feeling overwhelmed.