I don't know if it is the calipers, rather I think the the tiny pads that are deceivingly small.
For the brake shudder, try bedding them. I have had success with eliminating brake shudder using this process. I usually do it 2 times. I do it for new brakes or when I get shudder:
https://www.zeckhausen.com/catalog/i...Path=6446_6443