Then you're completely deleting the classic Batman and Robin dynamism.
And reopening the Batman/Robin gay debate.
Just bring Grayson in as a 14-15 year old gymnast/olympic wonder, give it the same dramatic treatment as Batman:TAS, put in a little bit of Miller's ASBR darkly tuned idiosyncracies, and you got your liveaction Batman/Robin scenario.
Let Grayson grow up overthe course of about 3 films, and then he becomes Nightwing, and the father/son relationshiop between him and Bruce has been developed.
Bring Barbra Gordon in around Grayson's third film as Robin in the series, potray her as the classic sexpot librarian, who is secetly turned on by the dynamic duo, pretending to have real purpose, if the joker hasnt returned by then, boom , there's his reintro, after a nasty rape scene, barbra gets the bullet that transcends her into oracle.
after that, you could introduce other expendable characters like:
Huntress:mercilessly bi*ch slapped by that perv the Riddler, then hung in the basement of the old "acme riddles" shop for kids.
Spoiler: shot in the head by that old dog, the PEnguIN.
Black Canry: bung-raped by Killer Croc and Man-Bat simultaneously, then smothered dto death by ClayFace.
Sarah Essen Gordon: caught in a violent lesbian menage a trois between Catwoman and Harley Quinn.
Then cap it all off with a final film: Batman saves Christmas!
Epic!