NTA. If you do want to apologize, just say you got heated from being put on the spot but shouldn't have asked him to pay, because the bigger issue is really the logistics not the money. Dragging two kids out of school and onto a 12 hour each way flight as one parent, plus being totally out of their routine somewhere, is a lot more difficult than your brother is thinking.

In my opinion, the gigantic pricetag on top of it is way too big an ask. My sibling and their very young kids couldn't fly hours to my wedding during the pandemic for all sorts of practical and logistical reasons, so we set up a video stream for them instead. There's other solutions for you to join in the celebration.