I am going out of my comfort zone and attempting to write a fictional story based in either the 18th or 19th century, but can't find anything online about my specific question. This could certainly be a dumb question, but firstly, could an uncle, if he had no heirs, or no wife, leave his estate to his nephew? I know that the Primogeniture law was a thing, but is that just if there is no written will? And secondly, if that is possible would it be frowned upon by the uncle's brother (nephew's father) to accept? Thanks! Hope this is the right place to ask this.
Primogeniture is a complicated animal, because it was the basis of English common law when it came to the inheritance of property, and yet wealthy men rarely actually passed the entirety of what they owned to the eldest son. Instead, they made provision for daughters and younger sons through conveyances and marriage contracts. I discuss the intricacies of eighteenth and nineteenth century inheritance in this answer from some time ago.
Uncles with no children could absolutely leave estates to their nephews. I also have a previous answer on the practice of adopting a cousin or nephew as an heir. However, in the situation you're describing I think the more appropriate thing would have been for the uncle to leave it to his brother with the assumption that his nephew would get it one day, or to leave it to his nephew with a life interest in it for his brother (which would be essentially the same thing, but the brother would have no ability to sell any of the land or touch the capital - he would just get the interest to spend and the land to live on and get rents for).