The main jets are being held in by the o-rings, and probably some crap that's build up over the years. Soak them with penetrating oil such as Liquid Wrench and in a few hours they should come out much more easily. To answer your question yes you can cover them with cloth and use pliers to remove them, just keep in mind that they're brass and therefore soft, and also as you can see it's easy to damage the carb bodies if you apply too much force, so be careful.
Carbs don't look too far gone in my opinion, I've certainly seen worse. There is a fair amount of varnish from gas on the parts, that can definitely cause the poor idling problems you were having.
If you end up needing replacement carbs, check eBay, or post in the Parts Wanted forum here, another forum member may have the parts you need.
For cleaning the parts, look around at your local auto parts store for some carb cleaner in a 1-gallon pail, they usually include a basket for dipping the parts, soak the small parts for about an hour and then hose them off with carb cleaning spray like Gumout. Also use the gumout to spray out the insides of the float chamber, and spray some down into any passages and holes you seek. Let everything dry thoroughly and you should be good to go.
More advice, keep the parts separated by carb and make sure that you reinstall them in the same carbs they came from.
Did you download a manual yet?
cheers
mystic_1
