If they came with Mareks, then you have Mareks now there. I'm so sorry as that's a tough one. I've heard some die, some make it, but it's always the ones we love the most that die. I have a friend on here that got it in her flock. She culled some, kept some, and now vaccinates her hatched...
So sorry to hear of the losses. :hugs That's rough but we learn from it and fix it so it can't happen again. Then our chickens can thrive.
I think I'd quit buying shipped chicks. That's what I keep telling myself about shipped eggs as not even half of them hatch x4 times I tried. Last year...