Grass is very hardy, and the sulcatas might like to nibble on it Bermuda grass comes in these big seed packages, you could planting some of that. It's also a hardier type of grass, but still might do better in a cooler spot
I know 2 tortoises shouldn't be kept together. I've kept a close eye on both of them to observe their behavior. At first my older tortoise did not like to share anything with the new tort but as the days went on they have kind of learned to live with each other. They both have their separate hides on opposite sides of the enclosure and they usually stay around their area. And most of the time we let them roam in our backyard and they always end up way apart from each other.
If I was to see aggressive behavior from any of them I would immediately separate them. But so far it's been calm and sometimes they sleep together. So I think I have been lucky so far.
I buy Bermuda grass already growing in big squares from the local nursery. that way it does not get stomped down and eaten before it has time to grow. one square will take root if you water it in the in door tank and does not take a lot of light. if they do eat it all before it starts to grow it is cheaper and better for them than greens from the store