Get chick starter and make it available to both moms and chicks. The moms will encourage their babies to eat when the time is right. Water should be provided that the chicks can reach, but place marbles or rocks in the tray so the chicks won't drown should they stumble into it. Chicks are extremely accident prone during this first week. Try to eliminate anything where they can get trapped or squashed. Make sure any fencing has smaller mesh around the bottom so tiny, curious heads can't fit through and end up being scalped by a curious adult chicken on the other side. (This happened to a baby chick I had, and I learned this lesson the hard way.)
The broodies and chicks should be protected from the rest of the flock, but keep a close eye on them to be sure there's no competition between them for the chicks.
Ideally, the nests the babies are in should be ground level, with sides not so high the chicks can't get out or back in. Yes, I would cut out at least one side of the boxes. Baby chicks aren't able to make jumps higher than just a few inches during the first few days. By one week, they will be getting quite agile, however.
Here's a tip. Grab a hunk of sod from your yard with the dirt securely still attached to the roots, and place it where the chicks will have access to it. During the first week, their immune systems are very receptive to good organisms in the soil that will colonize their guts and get them off to a really good start, and you won't have to worry about when and how to supply grit.
Then relax. The broody hens will know what to do, and the chicks will do the rest.