You should at least have a mineral block or a cuttle bone in the cage but it's best and most recommended to keep both the mineral block and cuttlebone in the cage.
The mineral block contains nutrients and minerals that the cuttlebone may not have and contain (like iodine) and it helps strengthen the bones and egg production. The cuttlebone helps maintains the bird's beak and strengthen feet, bones, beak, feathers and much more.
Both give minerals the other doesn't contain and it helps fill that gap.
The birds will eat the mineral block and cuttlebone when they need it. They'll eat it when their body demands it~
Grit shouldn't be presented to budgies. Many things could go wrong and can maks your bird sick or at risk. It's not necessary to give it to your birds as they already have their seeds, pellets, veggies and fruits and mineral/cuttlebone blocks.
The egg advice is already said by the others ^
Brocolli and dandelion leaves are great for your birds. You could also feed them things like apple (no seeds), carrots, kale, banana (sometimes), maybe parsley and much more. Just cut them up to biteable pieces for your birds. You could introduce these things by sprinkling a bit of millet on top of it and/or their seeds. They'll eventually love it.
Good luck and have fun with your new birds! They will really change your life as mine have. <3