Once she unhappily married him, it seems surprising that her brothers were let go from the mine due to their seniority on the wage scale. We never really heard why she left South Africa and him but is it possible that her brothers not being protected under the wealthy family umbrella contributed to the demise of the marriage?
I think that the mine owner was unscrupulous and had no intention of "honoring" any spoken or unspoken agreement to 'protect' his daughter-in-law's family at all. Her brothers made too much money so they must go. I'm also sure that the only reason that the mine owner approved of the marriage in the first place was because he saw some slight advantage of having Mr. Morgan 'on his side' when it came down to getting the men to accept his edicts. The Morgans were all pawns and they fell for it hook, line, and sinker. Angharad just had enough of the bullsh*t and called it quits...years too late, I'm sure.
By the time the Morgans were fired from the mine Old Mr Evans was dead (He was mentioned as the 'late') so the owner would have been Angharads husband..so it could be conceived that they were fired because of spite