@EmptyTheFrickingBins If I was expecting disabled members of my party to arrive any minute then I would have looked for a member of staff as soon as I arrived to get either another table or to get the overstayers asked to free up the table if they had been told they only had until our booking time.
Then it may have been sorted out before your parents arrived.
I am wondering if the reason you are struggling to accept being wrong is that you were maybe thinking of a general pub, just drinking, situation where 3 peoole seated at a table for 10 would be less surprised at being asked if ok to share. I can see why you would have been shocked at the outcome if it had been such a situation.
If I had been one of the 3 and IF we were supposed to have vacated the table anyway (rather than another having been set up for you) and you had disabled parents desperate to sit, I'd like to think I would have interpreted that as you trying to just get seated and not trying to rush us.
You can't know what the staff have arranged though. So when a reservation is involved (or for a meal even if no booking but you wanted to ask another group to share a large table) then best go via the staff.
But...
It was still not OK for the manager to publicly embarass you like that. I imagine the other party maybe described it as you asking them to leave but even then the staff member should calmly, quietly, say that it's best to let staff deal with fulfilling reservations in future.
Also, has anyone on the thread pointed out that if they really had another table set up for you, they should have removed your name from that one? The situation simply doesn't arise then.
If they didn't have another table and had expected the other party to vacate the table by 4:30, then staff should have been gently encouraging them to finish up long before you finally said something, 15 mins after your reservation time.
You were still in the wrong to have not gone via staff though.
I suspect that in a formal restaurant you wouldn't have dreamt of approaching the other customers yourself and that it may be the crossover between some tables being 1st come 1st served in pub mode and some reserved that had you (wrongly) thinking it was ok to do that.
TLDR:
The manager was out of order, and unprofessional, in her handling of the situation and a complaint to the chain about that is valid imo. She WBU in that.
But you would BU to not accept that you should have gone via staff in the 1st place. It should be possible to have your reasons why you thought it should be fine to do what you did, but to also accept, in hindsight, that it was inappropriate.
On whether to vote YANBU to leave after that public dressing down (regardless of how that situation was reached) it depends who pushed that decision. It was a celebration for someone's ruby anniversary. So I think the celebrating couples' feelings on it should have taken priority. Does "because we no longer felt welcome" include them?