Curate, connect, and discover
I think that instead of being super apprehensive about Jason and him dating Roy, Oliver should take one look at him and then one look at Bruce and go oh, I'm about to be so annoying.
Oliver starts being so nice to Jason. So nice. Inviting him to family dinners. Giving him both his hero communications and personal phone number and telling him to call whenever he needs something. He gives him new tech and keeps updating his weapons and armor. He helps with missions and clean up and says nothing if Jason is a little rough, apart from patting him on the back and saying good job. He starts keeping his picture inside his wallet and has other pictures of Jason, Roy and Lian framed in the house and tells everyone about him. He starts calling him son-in-law first and then just son and then calls him a Harper and eventually a Queen.
At first it was just to annoy Bruce, but after the first time he tells Jason that he did a good job and Jason starts to tear up a little, Oliver goes oh no, oh I'm actually doing this now. This my boy now. I don't care if he and Roy break up or something, this is my boy now.
Bruce still thinks he's just doing it for the sole purpose of pissing him off, though, and he is so fucking mad. The Justice League meetings have turned into a Cold War zone.
Bruce starts to being so nice to Jason as well, forcing himself to ignore some of the more outrageous things Jason does, and Jason is so, so fucking confused.