you have to assume they will not get along.. and you ideally need to quarantine the new one anyway.. maybe someone else who is better able can help the other..
No, they do not all fight. I myself have never had trouble with any of my Russians. That being said, any time you have more then one of any kind of animal be it human, dog, or tortoise, there will be times when fights break out. For that reason, the larger the enclosure and the more visual barriers the tortoises have, the better the chances of them getting along. Your thinking of getting another tortoise and that means you will have to be able to set up a second enclosure for atleast an isolation period. After that, you will always need to be prepared to have a second enclosure, if they do not get along.
Young ones do get along better with each other, but as they grow and become more sexual the troubles begin. Even as hatchlings one tends to be the more aggressive one who will bully the other one from the food and choice basking sites. Once more not always is this true, but it is more the norm.
I'm always the one to say separate them, but not all fight, there are exceptions to everything. the problem is, do you want to risk both your tortoises health and potential quality of life?
in a large enough enclosure, with hatchlings and a lot of stuff going on in the enclosure, you could give it a try. i would feed them separately, give them each their own dish. and basically double everything (hides, plants, ect) just keep track of their daily behavior i suppose.
I have a table made from a bookshelf with two adult Russians. They get along fine for now, but I do have two zoo med tortoise houses as a backup plan just in case they need to be separated. I'm gonna try and add a second female to the group this summer. There are a lot of tortoises that get along and a lot that fight, no way to tell until you put em together for a while.