If there had been no death before the fall, how would Adam and Eve's descendants have populated the earth, and would there be room?

This is theological speculation, but it can be reliable up to a point. They would increase and multiply as God said in Genesis 1, and populate the earth, with no death, until there were sufficient people and the earth could hold no more, whatever that number is. Then there would be a consummation, an end: God would take all those beings to heaven, and they would live in the heavenly kingdom with God, in that number, for eternity. That is the way we would look at it.