The children of an uncle who addressed him as brother-in-law should be addressed as elder brother-in-law's cousin or elder brother-in-law's cousin.
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.
Northeasterners generally referred to brothers as brothers, not specifically as brothers. This form of address expressed the relationship between men who were close and of similar age. In the northeast region, this title had been used for hundreds of years, and its meaning had not changed much. The specific way of addressing people varied according to the family order. For example, cousins could be addressed as eldest brother, second brother, eldest sister, second sister, eldest brother, second brother, and so on. In addition, the younger brother and sister would also call each other by their names. In general, the way Northeasterners addressed their brothers was an intimate and friendly way.
The child of the sister-in-law's father could be addressed as a cousin, depending on his age.
Your uncle's daughter should be called a cousin.
Nephew or niece referred to the nephew or niece of his wife's family. According to the information provided, a nephew or niece was the nephew or niece of a man's wife. This title was used to differentiate between one's own nephew or niece.
In ancient times, when introducing one's family members, they would often address them as young master, young master, grandfather, father, mother, madam, and so on. These titles all contained the demeanor of a noble or young master. Young masters and young masters referred to the children of the nobles, while fathers referred to the elders in the family, while mothers and madams referred to the female elders. These titles all had strong cultural implications. When used, they needed to be chosen according to the specific situation.
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 descendants of Gaozu were called great-grandchildren.