You can’t go wrong with that! I was a sucker (ok, got me…still am) for gimmicky/cool knives and flashlights.
The helicopters are a boatload of fun, too.
If they don’t geocache already, how about a startup geocache kit for father and sons? 
Edit: For your sister-in-law, what about home canning recipes, or kits? Does she can? Would she start, do you think? 
Also, I second the idea of the Leatherman All Purpose tool.
Brother and sister in law are both canning machines! They just moved from Phoenix to Oliver (interior of BC) and they’ve canned cherries, blueberries, greenbeans, and some other stuff that I can’t remember.
I’m heading there for a visit later this summer and I get to try all the goodies!
All guys like porn. You can’t go wrong with that.
Meh.
Reiman Publications publishes a number of magazines the adults might like. Reminisce has great articles (written by readers) about life before the 1970’s. Many are funny; all are upbeat.
There’s also Country, which has beautiful photos of, well, the country, with great articles (also written by the readers) at least one of which is always about a small rural church in the country. There are cooking magazines, etc., too.
http://www.reimanpub.com/
Or how about those awesome remote controlled gigantic balloon fish, I think they’re called Air Swimmers? Maxing out the Horror of Blimps concept. I think old guys and young guys would totally dig those. Hell, I want one. Or five.
I still think geocaching kits for your nephews and brother would be great! They already hike, and this would add to that! 
Young girls. It’s the gift that never disappoints.
That is a good idea. I’ve put it on the list. I’ll have to go through the whole gift buying thing again in December!
I think the 12 year old might be gay.
So he’s got a buddy to dish celebrity gossip with. And a beard to get him through high school.