Good for you - there are so many disabled pigeons who need homes.
Oystershell is just an added form of grit, so far as I'm concerned. We use a pigeon grit which is a mix of red and gray pieces (probably has oystershell in it) which provides the normal calcium and other mineral requirements.
Kinda depends on whether either (or both) of your residents is a hen. If so, you may get eggs anyway. If you do, and there's any oddities (thin shell, undersized) you may then wish to provide a calcium supplement.
thanks i bought both anyways since I am pretty sure they are hens...one laid an egg the day after rescue! but she wouldnt sit on it with the stress poor thing.
what induces pigeons to lay anyways? in captivity.....just curious