Rotts thrive in human company. A big yard is ideal but I would say a lot of interaction with family is even more necessary. A Rott left alone in the yard for long duration without any company is a recipe for disaster. I feel some natural area (even if it is a small yard) is necessary for all dogs and really helps their feet. However, irrespective of the space, daily walks are pretty useful for bonding with the family/owner and making the dog used to other sights, sound, people and animals.
Have you seen pups in person or on their web page?
In the webpage the pups look like 2-2.5 mo. They look good but it is hard to say anything without seeing them in person.
Rotts have a dominant nature and don't like to back off, so ideally they should be kept with a dog of opposite sex (with due care in time of heat / spaying and neutering is advisable). However, a submissive dog of the same sex who wouldn't fight with the Rott may be considered. Generally Labs aren't aggressive and if the owner properly enforces his alpha status then I would say that the two would be manageable.