Cyclops,
I hope you and your wife enjoy the experience. I sympathise with you regarding what others might think about the use of a wheelchair and then seeing the occupant rise out of it and seem to be perfectly healthy. My wife also has Multiple Sclerosis or in her case Periodic Progressive Multiple Sclerosis. She is healthy and can easily walk short distances but anything lengthy and she struggles. This year is a particular issue as we will shortly have to cross from T5 to T3 on our way to the USA and a wheel chair is essential for this part of the journey. Having said that my wife prefers to walk when it is possible and were we T5 only she would refuse to take assistance. Also we will politely say to the staff at ABZ that we do not need assistance there due to the short distances involved. However, we always require to book assistance as if there are flight delays assistance is essential to avoid the possibility of missing flights. As you are a gold member you are able to pick your seats at no cost. However, it is worth noting that providing one meets the highest of the three assistance categories BA will immediately allow seats to be booked at no cost for each person on the booking. Unfortunately we will no be able to use the upper deck as my wife really struggles coming down stairs and the steepness of the upper deck stairs rules this out.