Maat- Tap in your family name on Google you might come up with something. I found pages of my family that way. I was also able to find family in Canada and then email them.
Tap in your family name and the different countries they have links with. When questioning your family write down who gave the information. Sometimes it is good to record them for prosperity. Yes, it is going to be jumbled for a while, But as you get more information things will become clear. I have been doing this for many years. It is just like fitting together a giant jig-saw puzzle.
As regards to your great grandfather, try to get a description of him . That might be the best you can do and ask the elder ones who in the family resembled him. What you can do is write down the age he died and from what, if you know. Did he have any family other than himself? That might give an indication whether he was from India or local. Try ships records. I went to the record place in Kew but I found that tedious because I was not sure what I was looking for. I also joined the british library and researched the African Caribbean section after a lead from the internt. I also found information from the Ellis island records of family who had gone to the States in the 1920's. Without knowing where your family is from I cannot point to direct links.
I cannot stress how important it is to get descriptions: height, hair texture, colouring, distinguishing marks, work, anything they were known to say, habits.
I recently spoke to a cousin who knew our grand father and though I didn't know him. I am building up a picture of the type of man he was. Remember each relative would have a different perspective of the same person. Quiz everyone then go back again because onesession would stil something else and when you gleam informatin from a different person relay it to the person you are talking to. That might trigger a memory that was 'locked in.' Get a book and write everything down as you progress you will start to ask questions relationg to the information you already have. It is very rewarding because it give an individual a new sense of self and a deeper identity and belonging. It also makes the elders feel more vauled and gives them a connection to the young.