By “his son’s” do you mean “his brother-in-law’s”?
I think a lot of people thought that Kylo’s saber in the Last Jedi flashback was Luke’s old saber when really it is just the unmodified version of his crossguard saber.
are you sure? it makes sense that that lightsaber ended up being Kylo’s. “that lightsaber. it belongs to me.”
Frame from the Last Jedi:
But I do agree with you Collipso that it would have made a lot more sense for them to have young Ben use Luke’s old saber. Then it really does belong to him, but oh well.