My in-laws are very dependent upon my wife for their social and emotional needs. They suggested we go away for a couple of weeks AI for their 50th Bdays. I initially said I would after DW and MiL kept on about it and agreed we could all have our own space etc.
MiL asked which of the destinations I'd prefer and I said for her to choose a few but then show me the options if she didn't mind. She asked if I wanted her to book for me and I said no I'd rather book myself so I can check everything and handle the finances (neither a borrower nor a lender be).
Anyway she went and booked the 4 of us on a holiday without showing me first and asked me to send the money (2 separate rooms next door). She was surprised when I was annoyed despite previously agreeing that I would book for myself and DW. She then backtracked saying that it was to lock in a good deal and that it was just a deposit of £30 PP and that it could be cancelled.
Wife and I had not been getting on recently which was causing so much stress. So I decided I wasn't going to go on the holiday as bickering between ourselves around my via biased ILs would be a nightmare. I offered to pay the deposits and cancel.
It turns out she had put a £1000 down and it was non-refundable! Though she was too proud to tell me this after being offended at my backing out.
My reason for wanting to book myself is that I don't travel well and I am extremely tall so it's worth it for me to buy extra legroom. I also needed to ensure the flight times work for me as travelling halfway across the world home and then going back to work makes me feel worse than if I'd not gone on holiday at all. We may have also cut the holiday short by a few days.
Additional context: My FiL has been somewhat rude in the past and moody if we've spent time together (judgemental comments about our house - hates coming over - starts tending to the plants - won't take coat off or sit down and have a drink etc). Their way is always right apparently.
I think the problem is MiL secretly wanted to pay for DW without letting me know which would have been fine if she was open about it. I know my wife's personal finances are tight. She earns more than me but spends a lot more of her income so she definitely would not have the funds for a holiday (I've had to help her recently with money but that's now sorted). I wouldn't have expected this but it's all gone awry.