* Ladka ladki: This means a boy and a girl.
* Pati patni: This means husband and wife.
* Bhai bahan: This means brother and sister.
* Maa beta: This means mother and son.
* Sasur: This means father-in-law.
* Ladke ke bap: This means the boy's father.
The Solution:
The boy's father is the father-in-law, meaning the boy's wife's father. This means the boy and girl are husband and wife.
The key point is that the father-in-law (sasur) is also the boy's father (ladke ke bap), which establishes the relationship.