The daughter of her own sister should call her niece.
Your uncle's daughter should be called a cousin.
Uncle's daughter is my cousin. According to document [2], I can call her aunt or cousin. Therefore, my child can call uncle's daughter aunt or cousin aunt.
The child of the sister-in-law's father could be addressed as a cousin, depending on his age.
There was no clear answer to the question of how to address the Empress Dowager's sister. Therefore, I don't know how to address the Empress Dowager's sister.
Big sister and second sister are usually used to refer to the eldest and third brother and sister. From the perspective of their own generation, they could call themselves the " eldest daughter " or " second daughter." If one considered the overall family relationship, they could address the eldest brother-in-law, eldest sister-in-law, and father's brothers and sisters according to the different identities of their relatives and the differences between men and women. According to the English translation, the eldest sister could be called the "oldest sister" and the second sister could be called the "second elder sister".
The elder daughter could be called the eldest daughter, and the younger daughter could be called the youngest daughter.
Uncle's father could be addressed as his biological grandfather or grandmother, or he could directly address them as grandfather or grandmother. However, in some areas, people would address the man according to his seniority. The father of the uncle would be called grandaunt. In general, one could decide how to address his uncle's father according to personal habits and regional customs.
Father's uncle-in-law could be called uncle.
The eldest daughter is called the eldest daughter, the second daughter is called the second daughter, and the third daughter is called the youngest daughter.
The parents-in-law could be addressed as father-in-law and mother-in-law. In the written form of address, it was usually used as father-in-law or father-in-law, mother-in-law or mother-in-law. In their daily lives, they could address each other as father and mother along with their husbands. In addition, one could also directly fill in father-in-law and mother-in-law to indicate their relationship. As long as the relationship could be clearly stated, there was no mandatory rule in the law. If it was his wife's parents, he could just fill in as his father-in-law or mother-in-law.