Re: business class tickets
FOR the 10th of January. You don't want to wait until that date to make the purchase, which is how it reads to me.
I also don't like "the abovementioned flight."
Why not just be direct:
Please reserve two business-class tickets on UsingEnglish Airways Flight 1210, with a return on 10 January (preferably in the mid-afternoon) for Isaac Newton and Adam Smith. (I assume you need to provide the names of the people who will be flying.)
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.