Thanks for that first information. What I knew was unclear and kinda off mark.
His siblings in Pakistan are his half brothers and sister; my grandmother was the second wife. Only one of his sisters in Singapore is his full biological sister.
It's difficult to decipher the letters that my father actually received; they're old and fading. It seems though it was implied one of his brothers were sending a cousin to inform my father of things pertaining to the family. But they never met because my father was sailing at that time. That's the last contact they had. He never knew what happened after that.
So if you know anything else that would be helpful.