this would be my approach:
have them make an id here to ask questions which 100% sure they will have on week 2.
work with a lfs who does remote water changes to work with that sitter and be a physical backup source, and a water delivery source for 1 or 2 remote water changes which are cheaper than a redo.
Truly consider selling off your fish, that's the #1 risk, load and wear on a tank where the main keeper is gone, coral only or fish reduced tanks don't have things die while you are out and pollute the whole tank, sometimes rehousing or selling off fish preserves your entire system from mistakes whileyou are out this long, consider fish downsizing for sure as a hidden gem secret. with coral and inverts only a large tank is months self sustaining with no feed, and then just a few feedings means the risk drops and drops for algae issues while you are out. if some develop it doesn't matter, we can correct after return for sure but this will be the safest hedge against them.
squelch that tank metabolism and whole waste sinking down to coral only and any good lfs would house those fish for you if possible/large enough facility and give them back along with 2x free water changes