Remembered seeing a Prompt, where Danny is the step-brother of Damian. Talia had him on accident, before Bruce showed up to Train under the League of Shadows. Danny escapes, years later, Talia accidentally bumps into him and that whole debacle happens when the Batfamily find out about Danny.
So what if Marinette was Danny's Twin?
What I'm saying is - Talia birthed Danny and Marinette, but she didn't want them nor did Ra's wanted them either. When Bruce came, they took the chance to basically escape and disappear. They both kept in touch, however, and both found out about each other's Hero Identities which was great.
They kept in touch, they grew up - Good Parents Fenton, and Marinette finally catches Hawkmoth - and now they both have stable jobs and are doing great.
That is, until they both end up in Gotham.
And Talia ends up seeing the both of them - who are both now effectively gods now. Well, Danny is. I dunno about Marinette though, a Demi-goddess.
And of course, the Batfamily found out about Talia being there and spots her tailing two adults. And then Damian finds out about his cooler-older-half-siblings who are established superheroes (or ex-superheroes, depending) and have stable jobs and lives.
Damian has so much cooler older siblings - and they had no idea he even existed, or that Talia had another child. Either they dote on him, or act cold until Damian makes the first move to try and clear the air.
And THEN they dote on their youngest.
