buy big gifts and say it was because of the earnings from bitcoin

That would not convince them to use bitcoin since you are giving them expensive gifts. They will just be appreciative and tend to expect more gifts from you. Lol. Maybe just telling them what are the good things brought you by using bitcoins. Also just show them how easy it is to earn bitcoins. And then showed them your earnings with it. But in the event they still not convinced then try to explain it to others.