Most has been already said, anyway, my 2cents..
They will wander out of the box a few days after they open their eyes at 12-14 days. They don't need to stay in the nest, it will be their safe base for weeks though. At about 2 weeks they start to nibble on mums food, you can put a little oatmeal in the nestbox so they can start with that, buit it's not necessary. Mums normal food close to the nestbox is ok.
When they start to venture out - most likely you will not notice for the forst days they do it - it is important that they always can go back into the nest, no steps, drops, or tight spaces where they could squeeze into (like between hidy house and wall) should be within their reach. If you use a high walled nestbox you can either put ramps around, or tilt it on it's side then. Remember, in nature the nest is an earth hole, no matter where they go getting home is easy.
They are small. They fit through small gaps and holes. And, some of them can climb, much better than adults (some of mine kept escaping through an air ventilation slot on top of as 2ft high hutch door with hexagonal wire).
If you use a big water bowl, I would replace it with a smaller, shallow one until they are about 4 weeks.
With the nest on the second story I would relocate it to the ground floor and close off the second story for now if there is any chance they could get out of there, and not back up. Doe wouldn't be thrilled though, I put the does nose 2-3 times to the nest and restrict her to a rather small area until she fed them there, just to make sure she knows where the nest is.
Socialising...
If you want them to be used to humans I would start now, handle them a little, pet them in their nest (when they aren't hungry). and keep up doing that so that big, hairless ape doesn't come as a shock when they leave the nest, and they learn that being handled isn't something too scary and acdcept it. Depending on individiul characters, most still wont like it as adults, but there's imho a huge difference between being scared or just annoyed.
Imho, it makes a huge difference when they are handled early and consistantly.