I've been through this same argument with my mother and grandmother. I had the advantage of being over 18 and living on my own at the time, though. Once I explained it to them straight and to the point, they understood. That didn't mean they liked it, though. I think they wanted me to spend time with them more than they wanted me to be sitting in the church. I invited them to come with me hunting to see what I see and feel what I feel, but they didn't. In my mind, there's nothing inside a man-made building that can compete with the complete and utter awe I feel when I'm sitting in the woods surrounded by God's creations. Seeing the sun rise over the far ridge and the light filters through the trees and shows the wonder and complexity of the natural world that God created and gave to us is an amazing thing. It can push away all the stress of the world and that gives me a true feeling of appreciation for the blessings in my life. There's no time I feel closer to God than then. Keep trying to get them to understand that and maybe one day you'll succeed. Don't throw away the chance to spend time with them, though, no matter where you spend it. There will come a day when you won't be able to.