The Purva Mimamsa school doesn't accept that the names of individuals or gods in the Vedas actually refer to corporeal beings, but are limited to their etymological meaning, as explained in this post. For example, "Pravahani" means "one who carries things in an excellent manner", and does not actually refer to a person named Pravahani as the "son of Pravahana".
So if they don't accept Rishis, kings, and Devas as actual beings, then how does it explain their actions and behavior in the Smritis, Puranas, Mahabharata, Ramayana, etc?