I wanted to start the mission dead man's party from the expansion Hearts Of Stone, so to begin with, i went to Shani's clinic but the door is locked. Is it because of my level? couldn't enter the house no matter what i did i loaded older saves,came another time but the door is locked.

So you have the quest as active?
The quest marker for that quest points to Shani herself, but she is closer to her neighbor's door than her own.
Her door has a sign you can read. See pics.
If your at the right door, did you use the console or the mod to fast travel before you got the updates about Olgerd and Vlodimir.

Thank you for answer. I am at the right door but i didn't get any updates about Olgerd and Vlodimir. I just fast travelled to Oxenfurd and the door was locked. Do i need to Olgerd and Vlodimir updates to start the quest?

When you say you just fast traveled to Oxenfurt, was it using the fast travel from anywhere mod after fighting Olgierd, before you spoke with Master Mirror on the road. (where the regular fast travel sign is)?
Did Master Mirror give you the vial of von Everec blood?

I never started the quest. I heard this quest and i wanted to start while i was in Oxenfurt searching Siri, but when i went to Shani's clinic (using fast travel) the door was locked. So, i never had a chance to start the quest.

Ok, then. I havent done the Evil's Soft First Touches . Thank you for your answers.