I think the coach will be fine – if the passenger will be happier on the coach, I don't see the problem with it.

I can understand too why such a passenger would be happier on a coach: for one thing, one is in the presence of the driver at all times; for another, one surrenders one's luggage to the hold of the coach and then one doesn't have to worry about getting it off the vehicle oneself –.and since a person will be meeting the passenger (i.e. the passenger's son in this case) off the coach, he can take care of the luggage at the arrival end. My experience (observed) is that long-distance coaches, on the whole, are fairly good with elderly or other vulnerable passengers; train companies might be good too, but trains are more anonymous, and much bigger, so probably more daunting to many such passengers.