Personally, I will not totally understand your "predicament?" as I have no brothers. When at home I'm usually left alone. But that is cause I worked toward getting my family to accept the fact that I am that sort of person.

The point is this:
You are right in understanding and feeling that you cannot ignore your brother or his perception as that of some random stranger elsewhere. Even more so, if he is an older sibling. You never know what he will be discussing with your parents as an elder and adult. They will most surely, be discussing their concerns and worries regarding you, with him. Now you don't want him to have some weird idea about you. As you mention that he is a decent person. Everyone has multiple flaws. Even you may not be exactly saintly with your brothers/sisters/siblings. Something that you like, or some habit of yours, will most likely, maybe causing raised eyebrows in them. So you will have to be considerate and tactful in dealing with them. They are afterall, family.

That said, you cannot forget that all you have individual existence. A unique personality, an evolving character and personal preferences. A family often overlooks due the same fact: They are family, and so assume that they know you thoroughly. When multiple egos clash, there is bound to be some friction. You must strongly believe in own individual and thus protect it. You risk being sidelined as a immature "youngling" who can't be relied on to make a mature decision.

A person's image in others perception is hard to change, even more difficult in eyes of close relations. But this a good test for your ability to tackle such situations. You know what makes your brother tick or break. You could confront him head on and say that if he doesn't clean up his act and stay out of your way, you can adopt the same treatment, or talk politely and try to make him see sense. Its all up to you.

You talk about boosting self confidence and self esteem. Unfortunately, these are two of the most fragile emotions in a human. Think of making a Card House/Palace. It takes a really long time make, but not even a fraction of that time to crumble. Dramatic, perhaps, but true nonetheless. The only way you are going to achieve that is if you work towards it hard and steadily, not allowing anyone's comments bring you down too much, and if it does, then claw back up (love that phrase!). One thing I can tell you though... no one can help you make your self esteem. Family and friends, yes.. too a certain degree.. but no one breaks that self confidence like them (esp. family) either.

ah well...