They sound like real CFs - which should make it easier to say no!
I can't believe that someone has suggested that you rent them a house for 3 weeks.
Their DD can go to the library to study, if she can't use her school library - though some further edycation colleges in my city are allowing school kids to use their libraries to study if they don't have the space at home, so there may be other options.
Your husband offering her space at his office is very kind, but I'm sure that she can find somewhere herself, with family or friends. Noise cancelling headphones is something her parents can source, I don't think you should drop any over.
You can't stop the works, all you can do is make sure they're stopped at a reasonable time in the evening, so as not to disrupt her sleep, that's the key thing at this stage.
The neighbours may hold this against you, but it's unfortunate timing. You don't have to continue to placate them, and they've been so demanding that I doubt you could ever do enough for them to be happy.
You should look at local charity shops and auctions for furniture - lots of good mahogany and pine furniture going very cheap!