Are Taiwanese parents this mean usually? And stubborn?
Yes. Taiwanese parents hate everyone. I heard about one parent who disapproved of a guy their daughter liked because "his eyes were too big and too far apart".
I think this basically boils down to the issue of respect for elders. In most countries, respect must be earned. Here, you can just wait 30 years, and hey presto, you've got a whole load of young people kowtowing to you, even if you're still the same uneducated, opinionated, self-centred brat that you were when you were a teenager.
There are really only three possible solutions: your BF tells his parents to stop acting like spoiled three-year-olds, you move elsewhere and avoid all contact with them, or you break up. Personally, I would be inclined to turn up uninvited at some family gathering, give them all an extended lecture on what a bunch of backward, selfish old farts they were, and then walk away from it all. Obviously, that's not easy to do when you're emotionally invested.
btw, I suggest you don't send them gifts until they grow up. If they refuse to show you respect, creeping around them will just make things worse. You can't win people over that way.