You sounds like you are in a tough position since you seem to be pretty deep in the 'in' crowd - at least as much as your wife's family. You may have to just stick to your guns and site 'personal reasons' and not let it go beyond that. You could allude to the fact that it's too much stress, but I would site that as the main issue.
Trust me, they will push to have you remain on as MS, probably offering a reduction in talks, etc for awhile until 'you sort it out'. If you really want to, just force them to drop you from MS. Or as stated before, leave your name on the rolls, but accept no more talks, duties, etc. Once you stop going to meetings eventually they'll drop your name so as to not look bad for the CO. You WILL get questioned on the meeting attendance though.