Nervous and scared to be in triggering situations might not be such a bad thing, Jeff. In a way, those emotions sound better than nonchalance and over-confidence.
You are going into a situation where in the past you have experienced days and days of drinking, especially with your alcoholic brother-in-law.
You need a solid plan in place before entering that triggering situation.
Do you have a set of responses ready to your BIL's invitations (most likely repeated and repeated invitations?) to have a drink or get loaded with him. Maybe, do some mental role-playing in advance so that you are comfortable with your responses.
Do you have a plan for activities which only you and your wife can enjoy so that you are not constantly around the triggering people and places?
Are you staying in a hotel so that you have a place to which to escape if necessary?
Do you have SR set as one of your favorites on your phone or other portable device so that you can quickly log-in to talk?
Do you have a list that you can keep handy in your pocket which sets forth the reasons you do not want to drink?
Keep your mental game sharp, Jeff; spend time when you wake up (and often during the day) reminding yourself of the importance of sobriety; remind yourself of the joys and benefits you have enjoyed in sobriety; remind yourself of the things you don't want to lose.
Have a great and sober holiday.
Safe travels, Jeff.