This is sustainable if they don't have many emergencies and.or they aren't destined to live to say their late 90s. You could have another decade of this easily. if it is truly stressing him out and impacting his health or taking a toll on your marriage, I would figure out a compromise. Sounds like they are wealthy and have a lot of help. Are there aging professionals there who you can hire to advocate for your parents during minor/non-life threatening emergencies? Often those people are better advocates than family because they have worked in hospitals and know what is available and how to access it. That person can also inform you how serious it is so he knows whether to buy a ticket.

What else do the siblings have to do? I would see if there are way to ease their burden from afar.