Well, I can tell you that the lever under the stairs is for a decoration. If you notice you are standing on a gate at the bottom of the stairs. 

I know you said to not give you the answer, but I don't know how to explain it to you without kind of "giving" you the answer. Dont read on if you don't want, but these are the two places I found them.

1.) Go forward & up the stairs, take the key from the corpse on the table, take the right door, MAKE SURE YOU COLLECT THE ASHES FROM THE URN IN FRONT OF YOU! Enter the left side door, and head forward. You will now see a "doorway"- enter it. Click on the left side of the word wall. You will find a chest, but above it, slightly to the right, is a lever.

2.) Go back to the corpse on the table where you grabbed the key from and take a right again. Then, instead of going left like last time, go right and down the stairs. Once at the bottom of the stairs, head forward and you'll see a coffin. To the left of that is a small lantern "thingy". Right above it to the left a little is the lever.

Those are the only ones I know of. I have absolutely no clue where the last one is. Good luck to you though! :)

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