Is there an interaction between the Stamina of a host and a Parasite? The examples of NPC Parasite demons make it look as if the Parasite's Stamina transfers to the host.

The Parasite and Host each have their own Stamina score. Use the demon's Stamina for all demon abilities, no matter who the user is (which in the case of a Parasite is supposed to be the host anyway). Note: do not confuse "user" with "target". [1]