Adding more here cause I ran our of characters: Also, yes, '吗' usually indicates a question so you'd need a question mark, but sometimes it is an exclamation. In that particular sentence, I feel you can get away without it. It's like in English if you say "Are you ready yet, I am sick of waiting/we are going to be late." Do you need a question mark here? It would depend on how the person is saying it in Chinese. If they are annoyed and don't want to wait, they might say "[OMG} 你准备好了吗! exclamation mark" as a statement. Or they can ask it as genuine questions "你准备好了吗?"

I just wanted to say, there is actually nothing wrong with the way you wrote your sentences at the moment, so even though the other guy, Jerry, gave you some corrections, I can assure you they are not compulsory. Jerry did say that the second number 2 isn't clear on whether your older brother is coming home within the next 2 hours or after 2 hours, and I agree that it is a little vague. BUT the key is the word "才" which I believe Jerry missed. "才" is like "only" where it means exceeding expectation or normality, like "才7点" (It's only 7 o'clock), or "你怎么才来?" (why did you only just arrive now? [As in, how come you are so late?]). Since it means "exceeding expectation or normality", we know it must mean "My brother will [only] come home AFTER 2 hours." (because 2 hours is a super long time and we need to wait). If you wanted to say "My brother will come home within 2 hours" (ie, could be in half an hour, one hour, or one and a half hours, anything up to 2 hours) then you'd use the word "就". "我哥哥两个小时之内就会家." You'd have to add "之内" which means "within". "就" is like "just", or better than expectations: "I thought the trip takes 3 hours. Nope, my brother will be back in just 2 hours." For the other corrections: I can't think of a good English example but your Chinese seem to be okay enough to understand if I say this: The difference between what you wrote and what Jerry wrote is like this: (you) 我妈妈 and (Jerry) 我的妈妈. They both mean "my mom", and 的 shows possession (that the thing after it belongs to the thing before it) but native Chinese speakers would be lazy and leave out the 的 and everyone totally understands. So "了" and "有一个" in sentence 1 and 2 is like adding the 的 in my example, but not absolutely necessary and makes perfect sense without it.