To the best of my knowledge, Her Majesty's courts Service has not yet introduced any penalties for non-attendance at a probate interview.
Probate interviews are usually very quick and simple. It involves little more than swearing an oath (or, for atheists like me, 'affirming'). You're in and out of the door in a very short time.
http://www.hmcourts-s...orms/pa6_web_1109.pdf
However the point of the interview is to check that the grant of representation (i.e. the right to distribute the estate of the deceased person) is given to the right people. That can't be done if one of the executors named in the will isn't present (unless that person appoints an attorney, using the appropriate official form, to act on his behalf).
If your brother's ill health is deterring him from carrying out his duties as executor (rather than from simply attending the interview) it would be simplest for everyone if he renounced his right to take out a grant of probate. That just involves filling out a simple form. Your local probate office might be able to supply the form, otherwise you can buy one (for about £4 plus postage) from Oyez legal stationers. Phone 0845 217 7565.
Chris