Well, a hard-figure is not really required to cause jealousy and tension. Simply not struggling like the other family member is a signal. Or perhaps a nicer car, latest gadgets/tech, etc. Unless you never enjoy your wealth, people will notice it.

That's more a cause of the culture than the result of it, though. If all salaries were made public tomorrow, yeah, there's going to be the bit of occasional strife, but more than there is now over the long term? Hard to say.