How can a wheelchair bound disabled person prevent his butt sores from opening?

A friend of mine who has Multiple Sclerosis has to spend more time in bed and sit in a wheelchair during the day because of his condition.

He developed a butt pressure sore and despite his and his loving wife’s best efforts to regularly shift his position in bed and in the chair, the sore remains.

They are very much aware of the risks and dangers if this sore does not heal soon. If you have personal experience healing a pressure sore or know of someone who did, your tips and suggestions on how it could be done would be much appreciated, thanks.

Btw, my friend, 60, works at home sitting in front of a computer. He has limited body movement and most of the time uses voice command software.