In general I would agree with you, but you have to remember that Daniel is already about four times smarter and more rational than both of them combined. Tiffany is manipulating Daniel's very valid emotions to support her narrative of the day, because then she can blame the decision on Daniel. “Oh honey, I wanted to stay, but Daniel was miserable!” Or, conversely, she pressures Daniel to want to stay or at the very least feel guilty about wanting to leave because of his highly inappropriate, premature attachment to Ronald as a father figure, a false dynamic that she has encouraged from day one. Also, most parents relocate due to a work reassignment/job change, not international ass chasing. Neither of these losers work and Daniel clearly isn't in school, so he basically has nothing to do other than sit around and watch them make eyes at each other like horny teenagers. And I don’t think “I wish we could go back home where we had actual playgrounds and didn’t have to live behind barbed wire” is an unreasonable or bratty feeling to have. On top of everything, he went from living with his grandma and Tiffany’s adorable baby sister who he clearly adores to some deadbeat, dead-eyed rando who cheerfully tells him that he’s probably going to get abducted.
So no, I don’t think Daniel is the brat in this situation. Fuck Tiffany for her negligence and for prioritizing dick over her children.