People from different mother tongues marrying each other and their children speaking English at home is a fairly unique phenomenon from the last 10 years. 30 years ago those children were probably speaking Hindi at home.

Secondly, there is absolutely no correlation between those speaking English at home and those migrating to English-speaking countries. Almost everyone who has received a decent level of education has studied English in school. It’s not their mother tongue but it’s their second or third tongue - and that’s good enough to immigrate. Almost All university level education is in English. So the more educated people that you have encountered in your country have all studied a lot of their subjects in English