I don't know the answers to these questions - although I seem to recall that unlike in US slavery, children of slaves in the Roman Republic/Empire where NOT slaves themselves, they were freemen.
That said, the great estates were not long lived individually. One of the marks of the bad emperors of Rome (including the Republican "emperors" such as Sulla) was the tendency to combine purging of political enemies and boosting revenue by accusing the richest men that opposed them of some made-up crime, having them killed/commit suicide and seizing their lands. During succession crises (like the year of the four emperors), it was more likely than not that rich families would not be able to not pick sides, so a lot of such land was taken, and sold to other rich families (who then went on to piss off the next emperor, etc). In the process, the estates would be broken apart and re-combined, I suspect. Unfortunately, the History of Rome podcast (my primary source of knowledge on this topic) stopped talking about this other than "and so-and-so went on yet another purge" around the time of Caligula, when it literally became routine.
Grey Wolf