To the first part of this question, my answer is nothing, as in I don't say anything else to them, like ever. If they don't support me in decisions to better my life, then f 'em. Of course if this is a close relative and you think they will come around then that is one thing, but this journey is tough enough without someone giving you crap about it.
To the second part, if someone directly asks me I always tell them the truth. I just can't see wasting time trying to hide something I am not ashamed about doing. Of course I don't go blaring it from the roof tops, but I also don't hide it.
That said it is a personal choice, and everyone has a different take on this. Either way I think you have made a fantastic choice and I wish you all the best in your journey!!
