What do I do if the mechanism won't lower when I try to get into the house? I have the key from Vald and can't get up to the second level.

This definitely isn't supposed to work like this, but here's how I did it. I jumped on the fire posts out in front of the Temple, jumped onto the roof, and shimmied my way up as high as I could go. (A tip for this part: strafe around the corner of the roof, spamming space bar. You should slowly be able to get high enough.) Then, I positioned myself to face the porch of the Manor, and used Whirlwind Sprint to cross the gap. I'd recommend dropping a quicksave in case you miss; it saves you having to go through the trouble of climbing the roof again.