Technically yes it could, too much calcium can cause kidney damage and other issues. An all flock is good, or just a starter/grower will work too, as long as with either option you offer oyster shell on the side.
Yes you can. That's what I feed my birds and have for years. Common myth that laying birds MUST have layer. They don't need to if they have another source of calcium, like oyster shell. I have never had egg problems.
If you offer oyster shell on the side, the ones that are laying don't actually need layer feed. My recommendation would be to feed them a starter/grower or an all flock feed like Purina Flock Raiser and offer oyster shell on the side free choice for the ones that need it to take as needed.