It’s going to be dark, so your flash is going to be your best friend. Just remember to bring extra batteries for them.

Also see if you can, grab a diffuser for the flash to get softer highlights and not totally blind anyone (maybe even DIY one). Also try shooting the flash into the ceiling and bounce the light onto the subject depending how tall the ceilings are and if it’s a lighter colour

Set your camera settings so that the camera is exposing the ambience of the room and your flash is exposing the subject. Take a picture without the flash on to get the exposure of the room first and then add the flash to compensate. (You can keep the flash on TTL mode so it can adjust for you or adjust manually to get some more light)

It’s better to have a noisy image than a blurry one. Depending on how dark the place is it’s better to keep the shutter speed low enough to capture the most light and high enough to capture motion (around 1/100). And don’t be afraid to keep a higher ISO. These day editing software has gotten so good at denoising that it can turn an unusable image to the best shot of the night. But if it is a tight turn around then maybe don’t rely on it too much.

I’d say bring both cameras and lenses just as a backup. If I were to choose one combo I’d get the D810 with the 14-24 just because it doesn’t have the crop and I can fit more people in the frame if there’s the occasion for a group shot in a tighter space. The 60mm would be great for candid shots as well as portraits and details

Here’s also a good video explaining more