I have a question about Dwarven reproductive rates. If less than 1/3 of all men marry how can the family size be on average less than 4 children? Based on the LotR appendices (less than) 2/9 of the population of a given generation are married lady Dwarves. In order to have a stable population that means each of these married laddies must have more than 4 children.

But the dwarves don’t have a steady population. The problem you just described (plus warfare and displacement) is why the dwarvish population has been declining throughout the Third Age, and why Tolkien said the dwarves would eventually die out.