If they are not interested, they are not interested.  I would not push them.  Which will lead you to a tough decision: does all my vacation time have to be doing something that can include kids, or can I take some of that time just for me.  Tough call.

With my kids, we camped from the time they were infants.  Obviously an infant has no say in the matters.  I think that is important step in teaching ones kids to enjoy the outdoors.
If youy ar putting a teenager into an environment they have little experience in, I can see how they would be reluctant.  I mean it is a crazy idea, too anyone.  How can sleeping on the hard ground in a tiny tent, battling weather and insects, eating  less than gouremt food be enjoyable?  Hard to understand unless you have done it and come to realize  the food just tastes better while camping, watching a campfire is more entertaining than watching TV, etc, etc.