Pickled eggs: what am I doing wrong?

I’ve just run into a problem while trying to make pickled eggs and I feel like I could cry. I would appreciate it if someone could tell me what I’m doing wrong.

So this is my first time making pickled eggs. I’ve just boiled 2 dozen eggs. Hard boiled, 12 minutes, then left to cool in cold water. Like I always do. The eggs are 7-10 days old as I was advised not to use fresh eggs for pickling.

When I’ve started to peel them virtually every single one of them has come out with splits, bits of the white broken off, it just looks like a total mess and I don’t think I can use them.

I just don’t get what has happened, this is not the first time I’ve boiled eggs and they have never come out like this. Any tips would be very welcome.

I’ve added a picture of some of the eggs so you can see what I’m faced with.

At this point I think I will have to get new eggs and start again.

P.s Also any tips what I can do with 24 peeled hard boiled eggs are very welcome.