你好大家！请帮我把这些句子改好了。谢谢！

即便你没做错，你还是得冷静一点。
Even though you didn't do anything wrong, you still need to calm down.

我们的生命虽然不短，我们还是应该珍惜我们的时间。
Although our lifetime is not short, we still should cherish our time.

我有一个朋友， 她真是一位说唱行家。 他不仅会说唱，他还对它的历史了如指掌。
I have a friend, he really is a expert on rap. Not only can he rap, he also has a grasp on rap's history.

这里盖房子不是完全理想的，但是这里很安全，我们该想得开吧！
Building a house here isn't ideal, but it is very safe, we should be more open minded!

谢谢大家的帮助！

你好大家！请帮我把这些句子改好了。谢谢！

即便你没做错，你还得冷静一点。
Even though you didn't do anything wrong, you still need to calm down.

就算你沒做錯,你也要冷靜一下

我们的生命虽然不短，我们还应该珍惜我们的时间。
Although our lifetime is not short, we still should cherish our time.

人生雖不短, 我们应要珍惜时间

我有一个朋友， 她真是一位说唱行家。 他不仅会说唱，他还对它的历史把握了。
I have a friend, he really is a expert on rap. Not only can he rap, he also has a grasp on rap's history.
我有一友, 精於說唱, 不但如此, 他也对說唱历史略胜一筹
这里盖房子不是完全理想的，但是这里很安全，我们该想得开吧！
Building a house here isn't ideal, but it is very safe, we should be more open minded!

雖然在這兒建築屋子是不理想,不過安全可靠,我们思想应該開朗一些.

谢谢大家的帮助！

你好大家！请帮我把这些句子改好了。谢谢！

即便你没做错，你还得冷静一点。
Even though you didn't do anything wrong, you still need to calm down.

即便你没做错，你仍然需要冷静下来。

（Explaination: '还得' means 'you still need to' in some situations, like 'Even though you are good enough, you still need to do better....' [即是你很优秀，你还得更加努力], so it is usually used when you are trying to study harder, or to try again, which means more efforts to be made to make something happen. ’仍然需要‘ is more common and it won't be misleading.）

我们的生命虽然不短，我们还应该珍惜我们的时间。
Although our lifetime is not short, we still should cherish our time.

虽然我们的生命不短，我们仍然应该珍惜时间。
（Explaination: Well, yours is not wrong, this is just a better way to put it. '还应该' means  besides what you have done or what you have to done, you are supposed to do the followings. Here, the later part of the sentence wants to say something different from the former part. So, '仍然' is a good choice. last correction was made to avoid repeat. ） 

我有一个朋友， 她真是一位说唱行家。 他不仅会说唱，他还对它的历史把握了。
I have a friend, he really is a expert on rap. Not only can he rap, he also has a grasp on rap's history.

我有一个朋友，她真事一位说唱行家。她不仅会说唱，她还了解它（说唱）的历史。

（First, make sure you are talking about the same person. Here, '还' is used correctly to say something consistant with what has been said. As pointed out by other friends, 'has a grasp' could be clearly expressed by '了解' which should be followed by ‘说唱’.）

这里盖房子不是完全理想的，但是这里很安全，我们该想得开吧！
Building a house here isn't ideal, but it is very safe, we should be more open minded!
在这里盖房子并不理想，但是这里很安全，我们应该看开一点。

（'here' is not merely '这里'， especially when you want to do something or you are doing something HERE, it would be a good idea to add a 'prep', namely '在' in Chinese. 我想在这种一棵树。[I want to plant a tree here.] the rest is a little bit tricky and I will leave it to other people.）
谢谢大家的帮助！

You are welcome! (This one is natural and correct!)

你好大家！请帮我把这些句子改好了。谢谢！

即便你没做错，你还得冷静一点。
Even though you didn't do anything wrong, you still need to calm down.

我们的生命虽然不短，我们还是应该要珍惜我们的时间。
Although our lifetime is not short, we still should cherish our time.

我有一个朋友， 她他真是一位很會说唱行家。 他不仅会说唱，他还了解說唱的歷史对它的历史把握了。
I have a friend, he really is a expert on rap. Not only can he rap, he also has a grasp on rap's history.

这里盖房子不是完全理想的在這裡蓋房子不是很理想，但是这里很安全，我们该想得开看開一點吧！
Building a house here isn't ideal, but it is very safe, we should be more open minded!

谢谢大家的帮助！