Context first: My cousin, C, is living rent-free in the granny flat attached to the house with his fiancée, and has been for just over a year. It was intended to be "just for a few weeks" but ... 52+ wasn't originally the plan and they show no signs of moving on. He is a nice guy but a bit flaky and a total Mansplainer, which is annoying but dealable with. My Mum is in a nursing home recovering from a stroke. She owns the property and all the contents (except for some small items belonging to me, the bed, washing machine and sofa that C & Fiancée brought into the flat when they moved in). The flat is... poky at best, and with all their extra furniture and stuff it's tiny, but they seem happy enough in there (living rent free in Dublin I am unsurprised).
Today: C came home having bought a freezer without letting me know that he needed one or that he was thinking about getting one, and wanted to move part of the original furniture from the flat into the main house so he could fit the freezer in. I expressed doubt that I had space anywhere, and that I wasn't thrilled by this but he was adamant that he could "fit it in" and asked me not to call my Mum because it would stress her out. My Mum happened to phone while he was out in the flat moving the filing cabinet, and I mentioned that C was putting the filing cabinet into our house. Mum was very unhappy about this and asked to speak to C about it. Their conversation went on for a while and after he hung up he returned the filing cabinet back into the flat, and proceeded to complain that I had stressed out my mother by telling her about this plan. I explained that I was not going to lie to my mother, and he said about three times "I did not ask you to lie."
The question: I believe I did the right thing for my mother and myself by letting her know because as owner/landlady these decisions should fall to her - or at least get flagged to her before they are made, right? She was going to find out at one point or another anyway, better to find out and put a stop to it if that was her wish, right? Because I could see her wanting the filing cabinet going back where it was and C refusing because it's too awkward to make space in the poky little flat. Also, lies of omission are still lies, so he was asking me to lie to her, right? Was he right to be angry?
He and his father both have a better-to-ask-forgiveness-than-permissio