The other one is doing really badly. Since this photo was taken, it has lost the top full leaf and the half leaf in middle and only the cracked leaf is left.

It has no roots either. I have just kept it on the medium, because seller told me that will work.

I will get replacement plants, but I'd like to give a shot at rescuing these if possible.

Butterworts don't have very big root systems. Let the soil dry out a little and keep in bright light. I'm new to them as well.

Thanks.

That is what I have done, so far. Also lightly rinsing the root side of the one without roots with very very dilute hydrogen peroxide to prevent rot (on the suggestion of the seller).

The first one - with more leaves seems to be doing slightly better now. I am wondering if I should pull out the leaves that are dead or wait till the plant is better. As in, could they spread rot to other leaves or will it be too much shock for the plant right now?

Don't pull on the dead leaves. Sometimes they don't pull off easily and you can end up uprooting the plant.

What are those little white spheres in the media?

They seem to be Styrofoam balls. They are all through the media. No idea why. The plants came like that.

They probably act like perlite, provide aeration to the soil.