First of all thumbs up to your parents!
There are lots of details that need to be taken care of if you want to achieve “apartment-friendly” noise level, but it has been done (and it seems to me you are on the right track). That is, if you don’t plan on cutting aluminium all day using aggressive settings, because that is never going to be silent.
Using a water-cooled spindle is a part of the answer as you figured out, next up is going for a “quiet” vaccuum, and finally the tricky part is managing the air flows.
I think the recent thread below is quite appropriate, you should read it and maybe @holgersindbaek can comment on whether his enclosure has worked well for him in a similar situation than yours:
Then if you need to go to the next level, you could design one of those “box in a box” designs, but I have only ever seen them done around Nomads, not Shapeokos (that’s twice the effort and air flow may become a headache)
