Well,”middle class” is an anachronism. Joseph was a techne, which puts him into the working class. But in a non-money economy, a silver coin was not to be despised. Yes, I think Jesus was describing something he had seen.
The Lost Coin is a parable. There is no evidence that Jesus was referring to Mary specifically any more than lost sheep referred to her.
Luke 15:8-10
Re: Mary, Joseph, and Jesus being poor
While Mary was indeed humble we do not know if she was poor. She was betrothed to a respectable man with a respected occupation that required training and likely apprenticeship. ( Was a dowry needed in those times? ) She did travel to see her cousin. Presumably when the went to the inn to find shelter, they were likely prepared to **pay** for their night's stay in the inn. They were able to travel to the temple with Jesus when he was an infant and as a boy and I assume that they had the provisions to do this safely. They had the means to flee to Egypt and to stay there a long time. So? Should we conclude that they were poor by that day's standards? Personally, my conclusion is that they had enough wealth to provide for a reasonably secure working ( middle) class life.
Re: Working Class
The middle classes work but I will not quibble with you over working class or middle class. If you wish to call the family of Jesus a working class family that is completely fine with me.