I was gonna suggest to also add other lights outside of the car to light the interior from there as well. But your scene seems to be happening at night, right? That approach I was thinking of is more suitable for day light. But still, you can add an HDRI suitable for night scenes to yours. That still might help with the overall lighting, I guess.
EDIT: Or even just use Sun-Sky settings and set them up together with the tone mapping to mimic urban lighting at night. Damn, your situation has made me itchy to experiment with a scene like yours.
There are lights shining in from the outside to provide a bit "overall" light, or extra on the driver.
But, the ladies have the light on in the backseat to provide a show.
So now comes the problem of simulating a real world light in a DAZ scene.
Back when I started, I thought using a single prop with an emissive surface would be enough "I use just 1 lamp to light my room IRL, so it should work".
It can work, but not in every scene and it relies on reflective surfaces and a whole bunch of other stuff like I can't comprehend (just like IRL).
For example, this is one of my early renders using "SCENE ONLY" with just the bus stop light prop and a ghost light around that prop.
It works because the scene has other stuff that helps spread the light around, like the roof and glass of the bus stop, the back wall, the floor, and even the woman.
If I were to remove parts of the scene that are out of shot of the camera, the light would behave different.
But it also works because the light has space to go (if that makes sense), something not available in a cramped taxi.
Sure, now I would use more lights for extra flavour and probably spend way too long figuring out what effect I want .
"There's a car coming, so there's light from that. Also there's a stoplight, is it green or red? How big is the moon?"
I still use HDRI sometimes, but mostly at 0.2 strength with a subdued colour.
Anyway, lights in DAZ and getting that perfect scene you can almost see in your head, but constantly change your mind about, right?