Absolute zero is impossible?

Because of the ZPE, yes.

Even if absolute temperature is reached, there is no way to go further while the universe is expanding- so the entropy cannot go any lower ?

We will never reach that point. Even in a classical model we would only approximate it, approaching it asymptotically.

Absolute zero is impossible?

Even at absolute zero the energy of the system is not zero due to the ZPE. So "absolute zero energy" is not a thing even when you lack heat.

Even if absolute temperature is reached, there is no way to go further while the universe is expanding- so the entropy cannot go any lower ?

We will never reach that point. Even in a classical model we would only approximate it, approaching it asymptotically.