There are several possible reasons for why the 2nd tortoise isn't eating.
1) Maybe it's taking longer to settle into the new home.
2) Maybe it wants to hibernate. Sometimes a russian tortoise will slow down even when it's warm and there's plenty of light.
3) It's sick. If you bought the tortoise at a pet shop, it's probably wild caught and it may be suffering from being captured and shipped to America.
4) The enclosure isn't warm enough, or has enough lighting, or it's too damp, etc.
Look at russiantortoise.net/ for information on how to keep russian tortoises. Heating, lighting and water are very important. Also the right type of diet. Russians often respond to brightly colored foods. Yellow (dandelions or squash) and orange (carrots) are two good colors. Chop up some squash or carrots and spread it on good foods like endive or dandelion greens. Be sure to sprinkle a little calcium and d3 powder (Reptivite) on the food.
Also, be sure to soak the tortoises in about 1/2 inch of lukewarm water a couple times a week for about 15 minutes.
If the tortoise shows any signs of a runny nose, labored breathing, or has very loose stools, see a vet who has experience with reptiles. Even if the tortoise is healthy, it would be a good idea to go to the vet. Wild caught tortoises often have parasites that can get out of control in captivity.
Good luck!