We see Luke tell Leia about his parentage, but not Han....
Lots of ways do do it, of course, but I'd like to see it be a huge problem at first. Early in ROTJ, say Han was already kinda weirded out by the Force stuff and is really not over being tortured by Vader, so finding out that THAT'S who Luke inherited it from? He knows it's not Luke's fault and he doesn't WANT to be a jerk about it, but it makes his skin crawl. And Luke is coping a lot better than he was at the end of ESB but he's still not quite okay, either. But it gets better.
Han/Luke, ROTJ angst
Lots of ways do do it, of course, but I'd like to see it be a huge problem at first. Early in ROTJ, say Han was already kinda weirded out by the Force stuff and is really not over being tortured by Vader, so finding out that THAT'S who Luke inherited it from? He knows it's not Luke's fault and he doesn't WANT to be a jerk about it, but it makes his skin crawl. And Luke is coping a lot better than he was at the end of ESB but he's still not quite okay, either. But it gets better.