I can't comment on the health side of things, as each club will have it's own rules. However as you sign you life away on the disclaimer it probably won't be a problem!!!
What is most likely to happen is prior to the flight he will have a briefing from the pilot who will answer any questions your brother may have. He will then take your brother out to the plane and go through the checks explaining what he is doing and why.
They will then get in the plane and the pilot will explain the controls and dials to your brother. Your brother will have a headset so that he can communicate with the pilot and hear the comms with air traffic control. Once the onboard checks have been made they will commence their flight. Through out taxi and take off the pilot will be talking your brother through what he is doing.
Once airborne the pilot will continue to explain to your brother what he is doing, once your brother is relaxed the pilot will invite him to take the controls. Your brother will be talked through some simple manoeuvres which he will execute before handing back to the pilot. They will then return to the airfield and your brother will have a big grin on his face.
Generally speaking it isn't necessary to book far in advance as the weather plays a big part in these things. For a one off like this have a clear day with good vis will make the experience much more enjoyable. Once he has the voucher he can contact the club to pencil a date, and then confirm on the day whether it's a good flying day or not.
What part of the country is your brother in?