The additional post yesterday reminded me of something else with regards to the D'Silva (also Da Silva) connection, so in case you are still stuck just a couple of ideas. The Portuguese had a very different attitude to the mixing of races from the British, resulting (though not entirely due to them!) in a large number of mixed race (also known as Anglo-Indians) under the British Raj. They were marginalised by both sides but for some reason nobody has ever explained to me, managed to get almost a monopoly in the running and organisation of the Indian Railways (not the very top posts!)so if you have an ancestor who has a Portuguese name, claimed to be "European/Portuguese", was Roman Catholic and worked on the Indian Railways you can be pretty sure they were mixed race - but the Indian Railways were very important and efficient so it could be worth looking at "Indian Railways history" and seeing what archives might be found there. You also say that "one ancestor owned the Piska Tea Estate" but if you look that up it appears to have been a Roman Catholic Mission settlement run by Portuguese sounding priests. They would obviously have given employment to mixed-race people and were known for good record keeping - perhaps contacting the church (still there) might produce something? Good luck anyway.