It’s going all Silent Hill it seems!
We also seem to get our first look at Eva. She is clearly Rose not Eveline! Seems the Megamycete was able to resurrect Eva though only partly(lacking Memories of anything besides Ethan rescuing her) and only with Miranda’s own power.
The 4 Lords and Eveline are likely all present in the mental realm of the Megamycete.
I suspect the Duke knew that Miranda did not have enough power to resurrect Eva fully and thus wanted Rose to develop enough Memories to power Eva’s full resurrection which is why he helped Ethan take down Miranda.
As for why he wants Eva resurrected: surely Eva’s father was just as alive as her mother Miranda was! If the Duke is Eva’s father he would want Eva resurrected himself even if he must sacrifice his incompetent impatient wife in the process!
He is feeding every consciousness into the Megamycete just to get Eva back and he knows exactly how how many it takes to pull it off!