Since there are quite a few guppies who hardly know about family relations in Urdu I thought it would be useful to post a kind of relation dictionary English - Urdu. I´m sure I have missed a lot of relations here. There is one which I don´t even know myself as you can see below. So you are free to add more and I will edit this post to have a complete overview. (Mods, I think this deserves to be a sticky thread :D)
Sister - Behn
Brother - Bhai
Mother - Maa
Father - Baap
Wife - Biwi
Husband - Shohar
Son - Beta
Daughter - Beti
Sister´s husband - Behnoi
Brother´s wife - Bhabi
Wife´s sister - Saali
Wife´s brother - Saala
Husband´s sister - Nand
Husband´s younger brother - Dewar
Husband´s elder brother - Jaith
Mother-in-Law - Saas
Father-in-Law - Susar
Father of child´s spouse - Samdhi
Mother of child´s spouse - Samdhan
Aunt (Mother´s sister) - Khala
Aunt (Father´s sister) - Phuppo
Aunt (Wife of mother´s brother) - Mumaani
Aunt (Wife of father´s elder brother) - Taai
Aunt (Wife of father´s younger brother) - Chachi
Uncle (Mother´s brother) - Mamu
Uncle (Father´s elder brother) - Taaya
Uncle (Father´s younger brother) - Chacha
Uncle (Husband of mother´s sister) - Khalu
Uncle (Husband of father´s sister) - Phuppa
Niece (Sister´s daughter) - Bhanji
Niece (Brother´s daughter) - Bhatiji
Nephew (Sister´s son) - Bhanja
Nephew (Brother´s son) - Bhatija
Granddaughter - Poti
Grandson - Pota
Grandmother (Mother´s side) - Nani
Grandmother (Father´s side) - Dadi
Grandfather (Mother´s side) - Nana
Grandfather (Father´s side) - Dada
Great-grandmother (Mother´s side) - Parnani
Great-grandmother (Father´s side) - Pardadi
Great-grandfather (Mother´s side) - Parnana
Great-grandfather (Father´s side) - Pardada
Husband of wife´s sister - Humzulf
Husband of husband´s sister - Nandoi
Wife of wife´s brother - Saalehaar
Wife of husband´s elder brother - Jaithani
Wife of husband´s younger brother - Dewrani