Klemmers father is talking the truth. Helmut has no reason to lie. He's being diplomatic, whilst also respectful enough not to call out the person behind all this.
Someone who cuts their family out of a wedding and seeing their grandkids, is someone who is under the thumb (or very controlling and vindictive themselves).
Keep in mind that Klemmer can't even control his own social media (his wife controls it), and that paints a very clear picture of the sort of relationship they share. What makes everyone think he has control over other areas of his life?
His wife clearly hates Klemmers side of the family, hence forced Klemmer to pick them or her. Same with his mates, maybe he isn't allowed to hang out with them.
Now add into all this that her sister (who she is probably close with) lives in Newcastle, and possibly other people in her family. That would be the only family per se she has, and rather than driving 2hrs from Sydney to meet them, she wants to be closer to them. Enter arguements with husband. Enter "family problems", and enter the need to move to Newcastle because SHE has said so.
Thus would explain why Helmut is clearing his families name but not lighting a wildfire in the media by calling her out as the instigator in all this.