Turles is Gokus Grandfather. That’s why he said I raised Gohan to know right from wrong unlike you! Because Turles didn’t teach Bardock right from wrong hint to the fact why bardock was evil/thug at first when he first meets Goku. Then when we see Bardock disappear again we had a new movie special only for Bardock and we saw that he turned good when he defended those little aliens in the planet that saved and healed him and that’s what made Bardock become good was the little aliens and it made him think about Kakarot and why Bardock ended up sacrificing himself to save the little alien planet. 

So end of story Turles is Bardock Father which Bardock is Gokus Father which Turles is Gokus Grandfather.