Re: Multiple Sclerosis
Although I don't have any experience teaching Aikido to someone with MS, I have studied MS and treating its presentations with Chinese Medicine.
I believe Aikido can be of benefit as far as helping maintain joint suppleness and as a way for someone with MS to remain active. That said, people with MS need to be careful to not over-heat, or over-exhert themselves because there is data that shows a correlation between a worsening of symptoms when this occurs. If they are in a more advanced stage of the disease and have difficulty walking, or another more severe impairment, then a high paced class might not work as well for them.
They need to be aware of where their personal limits lay. That really holds true for everyone though.