I tracked down the raws and
@Fumettosa is right, all the stuff about a grandson is a complete fabrication. The "translator" just pulled it completely out of their ass, Yujiro says nothing of the sort. Even if you can't read Japanese it's a simple enough matter to transcribe the text into a machine translator and see that what Yujiro says is completely different.
On the page where this translation says "You both better make a strong grandson for me!", Yujiro actually says:
強くなりたくば喰らえ
Which google translates as: "Eat if you want to be stronger"
On the page where this translation says "It's your job to succeed where Baki's mother failed before, you better make my grandson stronger than Baki!", what Yuujiro says in Japanese is:
飽き果てるま喰らわせつつも「足りぬ」雌であれ
Which google translates as: "Be a female who is 'not enough' while being tired of eating"
You can glean the implied meaning from Fumettosa's earlier post, but the important thing is that whoever was translating this chapter was out of their mind. It's just flagrantly wrong, they didn't even try, they just wrote in whatever they wanted. I'm usually willing to put up with shoddy translations as long as I get the gist of what's happening but this is basically a rewrite. As disturbing as it is for Yujiro to be watching his own son get laid anyway, his character is still being completely misrepresented here.