Welcome to A2A, ydrasil. These are good questions!
About pubic hairs: There are no rules you must follow. Most guys do nothing with their pubic hair, and just let it be. Some shave it, though I think this is much less common now than it was 20 years ago. Occasionally guys might part-shave it into a particular shape, but few would bother. There is no need to comb it, because it doesn't grow long enough to tangle. So you will be the same as the other guys if you do nothing.
It sounds to me like your underwear is too small. No underwear should squeeze your testicles so much it hurts. You could try boxer-briefs in a larger size. Boxers give more freedom to the equipment, but shouldn't expose you when sitting or standing--perhaps this is just a fear because you are unused to the feeling, or perhaps it means you are wearing shorts that are too short. The print against your pants is something some people deliberately cultivate (and used to be common at some periods of history), but it can usually be avoided by not wearing pants that are tight or clingy.
I get the impression that you are developing and growing rapidly, but are in clothes, probably hand-me-downs, that are no longer suitable. Perhaps you are developing faster than your brothers did; perhaps your parents have just forgotten what your brothers needed. There are probably a lot of clothes available that your brothers have outgrown, but perhaps you now need some of your own. And there is a tendency for the youngest child to be 'babied' a bit, because people think of him/her always as the young one.
Most people leave body hair alone, except for facial hair. Most guys start shaving facial hair when it becomes too noticeable: at first only the moustache area, and only occasionally--eventually it becomes a daily chore. But most guys leave other body hair alone. Competition cyclists often shave their legs: it doesn't do anything noticeable to wind resistance, but it does avoid pulling on hairs when they get their legs massaged. Some guys who are very hairy go in for shaving or waxing for looks, but this is the exception rather than the rule.
Feel free to ask more!