To simplify it:
ABBA's first recording with the girls singing lead with the guys before they became ABBA. Here they called themselves "Festfolket".
ABBA's sound engineer Mikael B. Tretow
Mikael B. Tretow on wikipedia https://en.wikipedia.org/wiki/Michael_B._Tretow
This tune is called "Tune For Father". A little side note: see the building? Constructed with a log house building technique the immigrants implemented when they came to the US.
This tune is composed by my great grandfather. The late and very talented Klint-Olle is playing my great grandfather's tune.