I am a soon to be owner of two Sulcatas, they are 2" and still pretty young. I wanted to know if I can keep them outdoors full time, and if so, what is the best way to keep them hydrated?
Tortoises work best on their own or in groups of 3 or more.
As they get older and tussles for dominance start, there is no other tort to deflect attention in a pair. The loser in the scrap becomes withdrawn and ill and may die if you do not separate them quickly. The separation is likely to be permanent.
If you have three tortoises in a large enclosure with plenty of things to break the sight lines, then there are opportunities to hide out and avoid the dominant tort (who may be male or female) and this is less likely to happen.
In the wild, torts are largely solitary. They meet up to mate and move on. They don't get lonely and don't seek company. They look very cute as a pair when they are small, but we have to take care not to project human emotions on them.
At 2 inches I would be more worried about predators than humidity. Night time temperatures might also be an issue since babies don't seem to hold their core temperatures like bigger tortoises do. I started leaving my tortoise outside all day when he was about 4 inches. The pen we kept him in had a wire mesh top to it. He did have humid hide that he preferred over the non-humid hides that were available to him, but I am not sure what the humidity really was. Each night I brought him in and kept him in a closed chamber enclosure where I could maintain the correct temperature and humidity for him.
I would be worried about keeping such a little guy outside because they can be so sensitive. If something should happen to your heat source in the middle of a cold night, you wouldn't find out until morning.
I would not do it. I like to bring babies in at night. Too many things can go wrong when they are so little. And little ones need to be kept warm at night too. High humidity will not be an issue as long as temps are always 80 or higher. It will be an issue if temps drop below that at night. Low humidity will be an issue. Where do you live?
Pairs are never a good idea. Can you order a third, or cancel one? The torts will be better off this way. There is a thread explaining this in much more detail in my signature.