Welcome to the forum.
I did not play Divine Divinity since a very long time but i am going to try to give you some answers.
1) where can i find Sir Patrick's title deed in Verdistis? How can i get to his private chamber?
You can find the title deed in a secret room in Sir Patrick's house in Verdistis.
You can get in the house using a lever which is hidden in the garden.
2) i have the lockpick skill at 5th level and i cannot open the hatch in the alone house in verdistis.
Don't try to open it. This hatch will be opened later in the game. Don't worry.
Also how can i get to the stormfist castle? i went down the sewers an i only found one entrance to the treasure room and one entrance to the prisons. i killed the execuioner there but i cannot pick the lock both to the door that a guy is imprisoned and the door that a guard is next to it.
You can't get in Stormfist castle by the entrance of the prison.
There is another entrance in the sewers for the treasure room.
Try to find it by yourself or have a talk with the owner of the Ducal inn, he will give you a map of the sewers.
3)how can i solve the expose George's murder quest?
First you have to solve the quest of the people murdered in Vesdistis.
4)how can i solve the "get access to the tarts" quest in Verdistis? I found a place under the market (down a hatch) with tarts but when i go back to tell the guy that gave me the quest, the quest doesn't get solved.
You have to go in front of Corinna's house, there you will see women talking about the tarts.
I don't remember the names.
Then you will have to talk about it to the inn's keeper to solve this quest.