They had an archeologist explain it while standing on the second floor of a replica house. He said that historically the main floor was used to house the animals, and often where some family members slept, and the second floor was where everyone would eat (and often contained guest rooms.) He said the main floor would contain the manger (the feeding trough) of the animals. Because they were both of the house of David, they likely would have been able to house in the bottom floor of a relative’s house, or with relatives.

It made sense.

I’ve also seen other sources where they had the birth place to actually be a cave instead of a structure, because historically some people would use a cave as a place to house their animals. That makes as much sense as anything.

There isn’t a lot of detail Biblically either way. By the time the wise men came, he was in a house, but still in Bethlehem – that’s the first time the dwelling is specific.