Find Ancestors

Ok so I know this should be on the trying to find board, but they want me to pay. I've tried this before and got one responce but I'm hoping someone can help me. I'm trying to find out information on my Grand fathers family. He died a couple of years ago and I think it would mean so much to my mum if I could find anything out. My Grandfather was William Struan Robertson born in Dundee and one of 5 siblings. His mother worked in the same school he attended. His father, I believe his name was James worked out in India for part of his life, and at some point all but my Grandfather (who was the youngest) lived or visited out in India on the Railways. My Great Grandfather left his family, I think when my Grandfather was around 17. My Grandfather was a very proud man and his father was never discussed openly, this information I have found out through my Great Aunt and my mum. My Grandfathers siblings are Hamish (deceased David (deceased) Anne (deceased) May, is the only living sibling, last year she turned 90 and is going strong, but she is the only one left of the 5. I knew Anne and May growing up, I believe one of the brothers died a year before my own Grandfather went away, but again this wasn't talked about as my Grandfather had only remained close with his sisters. There is a rumour that my Grandfather had an uncle who lived in Australia, his name was William, and that my Great Grandfather was there at some point after he left his family. I would love to here an information anyone may have on this family to fill me in. Thank you Emma Humphreys