As much as you're not "allowed" to run a marathon without limbs. As much as you're not "allowed" to pilot an aircraft as a blind person.
zeropointone
I heard that "If my brother/sister/mother/father" story plenty of times. And it was never true. I've seen and heard too much while I volunteered in homeless shelters.
They want to continue living their lifestyle, just like OP. That's not necessarily selfish or entitled. It's just two incompatible ways of life. The solution is to cut ties and find people who are compatible, for both OP and his sister and her husband. Walking away in peace is always better than endless conflicts.
If they won't accept that then OP can't do anything else than moving on. I had to do that too with friends and relatives from higher socioeconomic classes. It's not possible to make people understand something they are unable or unwilling to understand. It's not possible to force people to have something in common with you. And that's okay. That's life.
Perfect altruism (Being selfless = destroying yourself) is not my standard. I consider it as destructive as parasitic behavior (Being selfish = destroying others). Extremes are always destructive. Balance is key. I think balance is necessary to come close to what people call fair. In this sense, a good/fair deal (win-win situation) is better than any gift.
Nothing beyond two kisses happened. That's reality. Possibilities are not reality, what-ifs are not reality.
Maybe deglobalization turns out to be a good thing in the end, it's hard to tell. But it's going to be rough.
Most do. But it's hard to blame them considering how painful such memories can be. It takes enormous strength remembering your roots. Most people never develop that strength.