Russian tortoise/greek tortoise

Question
do they get along?

Answer
It's not a good idea to mix tortoise species.  Each species carries its own particular pathogens which it has natural immunities to, but another species may not have the same immunity.  You might not have a problem right away, or ever, but at some point you might lose one or the other tortoise.  Even with the same species, you should quarantine any new tortoises for three to six months and preferably longer; even then, you are taking a risk.  In particular, Russian tortoises are known to carry the herpes virus (not dangerous to humans, but deadly to tortoises) and adding new tortoises to an established group should be done carefully if at all.  Another consideration is that different species have different breeding rituals--some bite, some ram, etc.--that can cause stress to a tortoise of another species.  It's better to keep different species separate.