I think that the likely culprits are acquaintances of nephew or possibly just other kids in the neighborhood. Apparently you can get info on how to pick locks just by going on Google; and an older house like Brother's with no alarm system is easy pickings. So Nephew wouldn't have known about it or condoned it, but someone who knew he'd be on vacation with his dad could have taken advantage of the situation.
DD says that sooner or later it will come out who did it, in the school gossip network but not for awhile. She's not as upset as I am because she's taking it as "I know the truth."
I agree with everyone who said that there's no use trying to convince someone who's already made up his mind. I texted my brother that since he felt that way we would just have to call it quits. DD will call her grandfather later and quit. She's just going to use dance team as a reason so it doesn't become a big family feud; the last thing I want is my father deciding she must have done it, as well.
The office manager doesn't remember talking about it to ODD, but she might just be saying that to get out of being in the middle. DD said it was an off hand comment along the lines of "Someone will probably be checking on his house" when the subject of Brother being on vacation or out of the office was discussed. So I'm sure that Brother has probably told Office Manager that she did this.
My brother then said he still needed to drop off payment for YDD but I told him we could not accept it. As long as he feels ODD was responsible then we cannot accept payment. We will take care of paying YDD ourselves. He's saying we were negligent in supervising his house key; ODD partied in his house; and we're in denial about accepting or admitting that. So there's no way we could accept a money from him. He's calling us liars and ODD a thief and a liar.
DH feels very strongly under the circumstances DD shouldn't have to interact with him. This was her last three days of work anyway. It's unfortunate but I don't have enough arguments. I doubt they'll give her poor references; they do work for my father.
I think he really thinks that we should just accept that ODD must have done this and he's not mad anymore, so hey, it's fine now. I'm not sure he gets that he just cut himself off from his two nieces. Ironically, if the situation had been reversed, he would have been furious (if it had been his older daughter.)
He didn't text back that he didn't think that or say he had changed his mind, so he's sticking to his belief. There's absolutely nothing I can do about that.
The whole thing about the longtime girlfriend is weird. My parents have met her at one of Nephew's sports events, but that's it. He never mentions her, never talks about her, he's so extremely secretive about it that it's odd. It's his business, but she does stay over the weekend, his house is on a main route so it's not like we're spying. We don't care. If you want to make her She Who Must Not Be Named, it's your business. The only reason I believe he might not be entirely forthcoming about whether she had a key or not was that he didn't seem that freaked out when I texted him "looks like someone has been in your house." You would think he would have said, "please go back and check the house thoroughly" but he didn't.
I can only control how we will interact in the future, which will be as limited as possible on our part.