In this situation I have been your brother, your brother's wife, and you, at different times in my life!
I'm currently in the same position as your brother's wife - DHs family puts a great deal of pressure on us to go back every year - in fact, in the past they've hinted that really it should be several times a year. And to be honest, like your brother by the sounds of it, we got fed up. We work hard all year and we only get limited holiday. We want to spent that somewhere relaxing and enjoyable where we can spend time together and have fun with our kids. Going to visit family isn't a holiday. It's going from real life to real life. There is no break there, and no relaxing! Actually we end up helping out a lot. We have made the decision to start going a lot less (once every three years, and not for our whole holiday period like we used to - half our holiday will be an actual holiday and the other half with them ). We deserve a holiday too. SIL actually mentions her new baby a lot when trying to pressure us to come back more and while we are fond of the baby, he's not our baby therefore I can't help but feel he's not a reason to sacrifice our family down-time each year. Going to another country just to sit in someone else's house and coo at their baby for two weeks isn't really my idea of fun, and while it's a nice idea for cousins to be close it's not really our number one priority in life above spending time together as a family. In laws are welcome to visit us but never bother and it does annoy me that it's us expected to spend all our money and use up all our holiday time each year to go to their house.
When I was in your brother's situation I think I went home once every 3 years as well. I felt like, what's the point of having this experience living and working away if I'm just going to fly home all the time?
My brother lives away, and I'd not dream of expecting him to spend all his money and time coming to visit. Long haul flights aren't cheap and like I said, going home to sit in someone else's house isn't really fun for more than a couple of days. He deserves his free time as much as I do and we are lucky to be alive in a time when social media and Skype etc means that you are never far apart from anyone, regardless of where you are physically located.
In summary - YABU!