My uncle was an only child, he had no siblings
My mother is his first cousin. On the paternal side there were two sons, my mum's father and her cousin's father. We are aware of all existing family on this side. On the maternal side there were 7 children, one of which was my uncle's mother, one adopted a child which I mentioned earlier and none of the others had children.
My mother is alive and she has a sister. Her cousin died before he could sign the will. The adopted child has died but he put his name on a birth certifcate for a boy who was 4 years of age (his wife and he re-registered the child's birth - his wife being the mother, the child was born 3 years before they married). We have a copy of the re-registered certificate (1990) but not of the original birth certifcate. We are not sure whether he is the natural father.