我父亲和我妹妹给我买了机票去纽约的机票。 我父亲和我妹妹给我买了去纽约的机票。

这是我的生日的礼物。 这是我的生日礼物。

我很高兴，但是我信觉得我们今年不能去美国。 我很高兴，但是我觉得我们今年不能去美国。

这可能是一个很好的好事，我有时间打算计划我们的旅行。 这可能是一个好事，我有时间计划我们的旅行。

这可能是一个很好的事不过这也许是一件好事，因为这样的话，我就有时间打算计划我们的旅行了。 不过这也许是一件好事，因为这样的话，我就有时间计划我们的旅行了。

I added some cohesive devices to make clear the relation between the sentences.

我已经知道这个旅行应该持续大概三个星期。 我已经知道这个旅行应该持续大概三个星期。

我已经知道这个旅行应该持续大概三个星期。 I had known that this trip should contain around 3 weeks. [ to me, It sounds like having a little bit wired.] 持续 -- contain In my feeling, 持续 in more time to describe a situation have been exits with a term/period. The rain contains three hours. These situations have been contained for a long period. rewrite this sentence to me, if you want to get better. and if you have any questions,welcome to ask me.

我已经知道这个目前我暂定这次旅行应该持续大概约三个星期。 目前我暂定这次旅行应该持续大约三个星期。

I guess that you tried to tell readers that what you had done for your travel plan, but past perfect tense does not exist in Chinese grammar. Also "know" as a verb is not quite appropriate here with its meaning; I would rather use "make a provisional arrangement" because you were making a plan. Other corrections were made to have the whole sentence more idiomatic.