This may be long, maybe not. I'm not sure yet, but here goes.
First off, yes, we are a selfish group. It's the sad truth, but the large amount of us go through life pleasing everyone by acting and no one else ever knowing how far we are going to please them. I know for me, I spent my own time dealing with things as I could, and pretended like no one ever had to know. But reality sets in eventually. So yes, we are selfish. But isn't someone with a gun to their head selfish to ask the person on the other end not to pull the trigger? If there's one thing we, as trans people, are selfish about in our lives, shouldn't it be something that makes us finally able to live life without hiding, without being depressed, or standing on that line where we just might fall off and end our own lives?
As for putting it off, how long would that be? I mean, if it'd been me, I would have called him out on that. "How long do you want me to put it off?" My wife and I had that discussion several times. I am putting off my transition so we can have another kid, because we can't afford artificial means. But, there were times I was asked to put it off until our current child (5 months old) was 18 and out of the house. Putting it off is ok, but with a good reason. If he's asking you to put it off just so he doesn't have to deal with it right now, then THAT'S selfish, the bad kind.
And I've been through the comments of "what will everyone think" or "how are we going to tell people", etc. etc. Well, you know what, hopefully everyone would think "as long as you're happy," but anyone who asks "what will everyone think" is one of those who won't give you that response. "As long as you're happy" is the positive response. "What will everyone think" is the negative.
I think we could all be in a worse place. Drinking/cutting/etc. as a way to get through things. Some of us have been there. I agree with you. That's no way to live. Sure, we are subject to a lot of problems after transitioning. Our unemployment as a group is one of the highest worldwide, but I'm sure some people who are unemployed are much happier being able to be themselves rather than working at a job and being miserable as the person they were. Honestly, if it wasn't for my wife and son, I wouldn't care if I'd lose my job over transitioning. If I was single, I'd have done it no matter what. Right now, my state is pushing for non-discrimination of LGBT at work, and that's what I really need to protect my job.
You must do what you need to be happy. Seems to me like this brother of yours is the problem. If his wife is supportive of you, then that means he's got a problem with it. From what you said, the rest of your family is supportive. Ignore him, and focus on those who are supportive. My direct in laws (her mom, dad, and sister) hate me right now. But two of her aunts and an uncle support us, and my friends all do, and my direct family does. I'm sure most of the rest of my family will support me. I have people who I will be ignored by, but focus on the positive people. I read a post yesterday about true, unconditional love. Well, there's your answer. Anyone who tells you that you shouldn't do it is putting a condition into the equation.