"and not be covers of another persons song or ballad. MacColl had his father"
According to those who knew MacColl and his father, the songs were being sung in the family long before MacColl "needed" such validity - I'm sure the cinema queues in Manchester in the 30s did't care one way or another.
The indication was that MacColl knew these songs all his life in one form or another.
The need for such "validity", to my recollection, is very much part of the latter days of the revival, where many people are claiming to be traditional performers o the flimsiest evidence.
MacColl, at no time in my hearing, claimed to be a traditional singer, as many revivalists have on the basis that they heard "me Granny sing 'Knock 'em in the old Kent Road' at one time'
The somewhat spiteful claim that he invented them has no evidential validity and, compared to songs that were being found throughout the latter half of the 20th century, there is no reason at all why they shouldn't have been sung.
I certainly heard his mother Betsy sing on numerous occasions - or was it all a dream maybe?   
Jim Carrroll