So you can go away for the weekend... this is how I deal with it. The week before eat really well, lots of fruit and fibre, and take a laxative the day before you go away so you are 'empty' enough to stand a couple of days without going. Then you don't even have to think about it while you are away. You can fix everything over a few days when you return home. I hate messing up my routine doing this but it is the only way I can go away for the weekend without going crazy. Try this. As uncomfortable (mostly (for my brain ) this is, you certainly won't be worse for wear physically for not going for a couple of days if you've been ablt to be 'regular' the days previous.
P.S. if this visit is no fun for you because your family is how you described, maybe that's reason enough not to want to go visit.