Welcome, Tristoon <img src="/ubbthreads/images/graemlins/wave.gif" alt="" />
I am sorry, but my French is too bad to explain. I hope, you understand English (there is a French section for BD).
the warehouse =>
http://www.kiya1.de/beyond/act3screens/Act3Waredoor10.jpgyou will find the key a few steps north in the garden with green crystals, press the ALT key to see it. It is near a bench.
http://www.kiya1.de/beyond/act3screens/Act3key0.jpghere is a picture link of the key.
The stone => there is a grave EAST of the church: Anbuklar's grave. Take the mirror out of it and place it in front of the church door. Then go to the stone and click on it. It should stop as soon as you see the vision of the church.
http://www.kiya1.de/beyond/act3screens/Act4Anbukgrave0.jpghere is a picture of the grave, where you find the mirror.
Closed church => have you met witch Kiya? Did she challenge you to a duel? I need more information. If I understood you correctly, you had a rank in the book and now you have none? Did you come out of Kiya's crypt? If you did => there is a messenger there, who tells you, you have an invitation for the church. Please, look there again and click on this messenger.
Kiya
http://www.larian.com/ubbthreads/postlist.php?Cat=&Board=BDHintsFrenchand here is the link to the French section of the game. I'm sure, gamers can help you in your language there, if you can't understand what I wrote <img src="/ubbthreads/images/graemlins/wave.gif" alt="" />