Sister's daughter is niece
It means: "How do you say that they are beautiful sisters?"
YesThe son and his sister = 1 son, 1 sisterThe sons and their sister = many sons, 1 sisterThe son and his sisters = 1 son, many sistersThe sons and their sisters = many sons, many sistersThough in reality this is a strange way to say it. More normal would be "The sons and daughters".
'Makan' is the English word 'son' in Malayalam.
nia / mac deartháir (brothers son) / mac deirféar (sisters son)
my sisters x
Estas son sus hermanas (if you meant "these are her sisters").
Brothers and sisters have I none But that man's father is my father's son. (Who is that man?)