I think BIL thinks that my MIL somehow sweet talked FIL to not work on Friday out of spite. And there may be a bit of a grain of truth to that. Moreso, it's about needing the help of setting up a home to host 6 people for dinner, breakfast and lunch. That's not exactly a small undertaking for someone who has problems just walking.
Heck! Who doesn't want to retire as early as possible? Even if it is just one extra day, lol.
Seriously, though. I am so appalled by your BIL. Aaaahh, WTF!?!? I know I'm preaching to the choir, but retiring is a MONUMENTAL, positive event in someone's life. And BIL is taking away some of that celebration and joy, by upsetting everyone over nothing. His selfishness and ridiculousness is overwhelming.