Wonderbats and Dick/Stevie
I liked the Batman and Wonder Woman moments in Justice League, so I think they can get together in a world where Bruce is a little less troubled and closed off.
After the mission, Diana can work as a liaison for a charity art function that Bruce is funding. They spend more time together, getting to know each other and becoming friends. They'll also get into some of banter over time, similar to the show. At the art event, which an go off with few problems (I don't know if someone will crash the party), Bruce and Diana can share a dance. There could also be a moment where Diana is buried due to an attack, and Bruce tries to dig her out, like in the Justice League pilot. This could also be a turning point from their feelings from friendly to romantic.
It would be a slow burn since Bruce is still Bruce, and Diana now also has to think of what being in a relationship with a civilian would mean. She could maybe get advice from Clark and Barry.
Bruce may also try to push Diana away from him once he realizes how much she means to him. Once it becomes clear what he's doing because Wonder Woman is smart, Bruce can be more direct and blunt, listing all the reasons a relationship between them would be a disaster and detailing each of his flaws.
Nightwing can maybe explain Bruce to her at some point.
Eventually, with the two stubborn personalities and Diana showing that she's not going anywhere, Bruce finally caves and lets her in a little.
As for Dick and Stevie, they'll grow closer professionally and as friends. Their relationship will be a slow-ish burn, as well; however, they will be more open and less stubborn since they are both more emotionally mature and Stevie is pretty adaptable and open-minded. They'll take their time more so because they're trying to find a work-life balance, acclimate to big changes, and figure out if they're willing to risk their friendship by taking it to the next level.
Bruce and Dick will both experience teasing from the rest of the family, and maybe some other hero friends.