To my "ear" they sound fine. I've heard people say these very sentences - but that does not make them correct.
To my "eye", however, it's another matter.
You repeat the word "about" twice in the first sentence. I wouldn't do this.
Please decide about a topic you want to discuss in the next meeting.
Is it possible to get us a temporary login to the website?
I just saw your twin in the mall (only if you were inside of the mall). Otherwise, I would say - I just saw your twin at the mall.
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