Facts, just the facts. If your friends drinking isn't an issue for you, then tell them thanks for their concern and sensitivity but you are truly fine. Then leave it.
What they decide to do, beyond that, they are doing for themselves. Maybe they are having some of their own thoughts or struggles with substance use or abuse.
You neither need to feel guilty or insulted by their choice of behavior, no more so than they should be by yours.
If you do find yourself strongly reacting to their choice as to how to behave around you, it might be enlightening for you to ask yourself why.
or you could let it go and enjoy your yearly trip without making drinking or not drinking an issue in either direction.