I'm so sorry to hear about your son's passing. Do you have a link to the charity event/a charity page for your son? I look at my son and think that if anything were to happen to him, I'd want everyone to know his face and story, to keep his memory alive. It seems you are doing just that - I don't have the words to say what I want to say, but I just wanted to let you know that this internet stranger cares.
In terms of your questions -
I'd go the D610 for maximum low light capabilities. Usually I'd recommend the 35mm for an event, but since it's a DX only lens, the 50mm should do fine as long as you have a decently large room to shoot in.
You should absolutely bring your flash. Play with it during the day, before the event starts. I bought my first flash hours before I had my first professional photo shoot because I was shooting in the client's home and wasn't sure if they'd have enough light. I played with it and worked it out enough to successfully utilize it at the client's house. The photos turned out beautifully. My suggestion to you is, since you're new with flash photography, point it in the other direction or to the side of your subject and bounce it off a wall. It will give you extra light without altering the lighting characteristics too much. It's better to have the flash and decide not to use it than need it above all costs and not have it. I don't recommend using the built-in camera flash - it's way too harsh, even when turned down. If you have to use it, put your fingers or a piece of card in front of it to dim it as much as possible.
As for the lens hood - you shouldn't need it, no. I wouldn't bring it.
As for low light photography tips - put the shutter speed as low as you can without noticing camera shake (I usually go to 80 but my camera equipment is much heavier than yours, so perhaps you could get away with 60? Depends on your steadiness). ISO second.
Bring the flash. Seriously. :)
I wish you all the best! Good luck at your son's charity event and I hope you guys raise a ton of money for a great cause!