Do you make things ? as in household stuff, I mean. Decorating, laying carpets, new flooring, bricklaying, slabbing, that kind of thing ?
Make them feel useful, even if it's just as an extra pair of hands, and they'll soon start to build up the hand/eye/brain connections. Take them (or at least the eldest) with you when you go to buy supplies. He's there to help you, but you'll probably need to be quite clear about what help you need to begin with. Quietly just explain from the ground up. No experience, then he's ripe to learn, to pick it up.
If you can't make him enthused about being active, you can at least encourage him to be practically active.
Thing about that kind of learning is though, that when the younger one comes along, then the elder one is encouraged to reafirm his own knowledge by teaching him.
I am minded of a conference I attended several years ago. There was a very bright and bouncy and cheerful and incessantly upbeat young lady expounding the belief that the majority of children that we would interact with needed hands on experience to learn. That they were Kinesthetic learners….and since we were all hands on people we should use that with all the groups we taught since they were in the majority and the other types of learners had kinesthetic tendencies as their secondary learning methodology.
Then I added up her figures……the largest single group might be kinesthetic learners, but the other two main groups outnumbers those learners. Auditory and Visual learners are often encouraged to be kinesthetic learners when that is not how they actually learn best.
Humanity learns from listening, from seeing, every bit as much as from 'doing'.
I am rarely a fan of youtube, it has just so much dross, and life is busy and all too short, but, and it's a big but, there are an awful lot of people whose opinion I value who post their carefully selected links. Those might be worth while finding and perhaps emailing to your nephews. It's a good way to absorb learning that does encourage people to 'get out there and do it'
M