So sorry to hear about the losses. It's particularly sad, somehow, to lose kits to squashing, but some losses are to be expected. It's just the way things are with rabbits.
I think i know why the runt is the runt... it had poop stuck to its bum. It was hard to remove (lots of soaking with warm water), and it was so stuck it couldn't pee. Poor baby. So, now the runt is clean, has some food in her belly, and is exhausted. Cross your fingers, everyone
Well, runt made it through the night, and has a full round tummy. But his head and neck are miniscule compared to the rest. And his bum is coated in mess again. I'll clean him up and see how he makes out. I may end up culling him if he has stuff caked to his rear tomorrow.
It had a digestive issue, and had to be culled last night. It was 1/2 the size of the rest of the litter, and dispite having a round tummy, still hadn't grown even a smidgen. I would have likened it to a peanut baby, but it had normal ears and head ratio.
I think you did the right thing. I had the feeling it was not going to improve, but it's hard to suggest to someone that they euthanize a kit without more to go on.