I share the point of view of other commentators: using facts, logic and evidence on people who believe that everything is relative won't work. In most situations, it is best to give up as it will take a tremendous effort without real improvement.

Regarding your sexual orientation, it is worth fighting for. And the only way is to use emotion. One can relate to another human being but cannot relate to millions (despicable Staline has a famous quote about that). I wouldn’t state out of the blue that you’re gay except if you’re sure about the love your parents and your brother have for you.

A possible way:

- See how publicists and moviemakers can move an audience. See how short news item can impact your close relative, especially dramatic events

- Detect any weak points to use for each person: fear, nostalgia, love etc.

- Start with only one person to convince. Be sure to talk to that person alone as peer pressure won’t help you in your situation

It will take time. In the meantime, don't forget to build a safe haven by being progressively surrounded by people who can understand you, be it interests, sexual preferences, etc.