1) can he do the job? Most of the folks around him not only think he can do it, but do it well. So that one can be laid to rest (easier said than done, I know, but just for the sake of decision-making).
2) will he have to stay longer than he wanted, to ensure the company ‘gets its money’s worth’ from the training they provide. That’s a decent consideration – what if he paid, or helped pay, for that education? Would that relieve the perceived burden of paying them back? Is that even an option? Perhaps talk to the owners about this particular concern, and see if there is some way he could offset that training cost. Such as, ensuring that whoever replaces him is trained by him, rather than going to some paid training sessions. Something like that.
3) The existing job is stressful, and the new job would be stressful. And I would hazard a guess that if he didn’t take the job, and some bozo did get the job, that would be stressful as well. So perhaps instead of thinking about avoiding stress, what are the exact stressors of each? Are either sets of stresses, something that could be modified or reduced so that they aren’t such an issue? Alternately, is he a good one for taking care of himself and does he have decent stress management skills? Since “stress” is an issue with all of the possible options, perhaps dealing with that monster head-on would be valuable no matter what happens.
4) would you be able to make his new suits, or do you know of some talented seamstress who could? Maybe turn that investment into solid work for someone who could really use it. Then that becomes a win/win too.
I agree it has to be something he feels good about, or none of it will be worthwhile. If the above issues can be dealt with, would he enjoy it? Perhaps talk to the owners, who seem very open to such communications, and tell them he has mixed feelings and why. Perhaps they can help him and/or your family forge some alternatives which will make everyone happier. A nice big paycheck with lots of strings attached isn’t much overall improvement to quality of life. A nice new big paycheck with some tweaks to make it more comfortable, is a much better deal for everyone. Custom fit this job, like his tailored suits, and it will be easier to wear. If it can’t be tailored, then it probably doesn’t fit. My $0.02 anyway.