Yep, I've worn 2, although not often, and I'm not an expert.
I think by far the easiest way is too put one on your front, one on you back. While the new baby is still tiny, I think I'd consider investing in a woven wrap, buckle (like an Ergo, Boba, or any one of the many out there) or mei tei and wear your older boy on your back in that with your little one on your front in the ring sling. Generally from what I've seen, it's easiest to put the ring sling on first, sort of partially adjusted, then put the bigger kid on your back, then put baby in the ring sling and do your final adjustments.
Depending on your kids you could definitely wear them in the pouch and ring sling too, with the new baby basically on your chest and your older boy in a hip carry. I don't think it would be super comfortable for very long, but if all you need is a quick up and down to assage any jealousy, it should work just fine.
If you're willing to go down the babywearing rabbit hole that is The Baby Wearer Forum, they actually have a whole forum on wearing more than one. It's not particularly active, but there's a lot of information there if you go back through the archives. http://www.thebabywearer.com/forum/forumdisplay.php?59-Wearing-More-Than-One
If you want to actually see how it's done, just go to youtube and search tandem babywearing. There are a bunch of videos demonstrating different options for wearing two. Obviously, as with anything else baby related, just use your own judgement and if something doesn't look safe or comfortable to you, trust your instincts!
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