Greetings. According to the exorcism quest, i've found the diary, the mandrake root, the Holy scriptures and the holy water yet i cannot perform the exorcism. The dialog options do not change. How do i get the quest?

You also need a Rosary (can be bought from Erbert of Trimoli in East Glatzburg) and the Mandrake Potion (Enrie Jungwirdt from East Glatzburg can brew it for you from the Mandrake Root).

Since Duchess Yulliete is of higher nobility, you need three proofs against her. The first two proofs are the confessions from Ethien and Raimond after torture. The third proof is the witness account by gravedigger Dietrich. Speak to the innkeeper Wanda Gielwitch to obtain the note that the gravedigger knew about the evil befalling Glatzburg. Find a small house at the left side of the Glatzburg cemetery and interact on the doorway. Agree and do what the gravedigger asks and he will come out and provide you the third proof after questioning.

thanks, i've completed the quest. Now off to the Pagan temple!