The significance of Joe Biden's plagiarism? , the answers to your questions are already on IPBiz, and elsewhere. Biden's father was some kind of used-car salesman, and was not a coal miner at any time in his life. Various members of Biden's mother's family had gone to college.
As we watch the polling trends in the last week or so, we note that no one really cares about Joe Biden's plagiarism (the clearest example of which was copying five pages of a Fordham law review article while at Syracuse Law) or Joe Biden's misstatement of facts (in his use of the Kinnock speech as applied to Biden; or in his famous reply to Frank). Frank doesn't care about what Biden did, nor does anyone else.
Plagiarism is no obstacle to arriving one heartbeat away from the presidency. But the Glenn Poshard story already foreshadowed that reality.