[ojnabieoot]

The idea of multicellular life on Ceres is implausible for the reasons you mentioned, but there could be something like archaebacteria or other extremophiles with very slow metabolisms and which don't reproduce very often. As it's a brine ocean, the water could be chemically "hot" enough that a form of life is sustainable in a bio-geological cycle.

Here's an interesting article exploring the lowest possible temperature for life on earth (which is largely focused on vitrification blocking cellular metabolism but has both theoretical and empirical insights): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3686811/pdf/pon...