You'll have a better chance of them getting along if raised as babies together, but all in all Sulcatas do great as being the only tortoise. They actually do not need "friends" or other torts around them.

50/50 chance if they will get along or not. You may notice some ramming behavior or one trying to flip the other one over.

I'm still introducing my 2 year old to my 4 year old and I do it always under constant supervision.

Hope that helps a little.