I could climb the wall and flip the switch, but something tells me I would just get sprayed with acid (again). We could check the floor for pressure plates.
The DM (

) was pretty clear that we found no pressure plates. So far the best option sounds like the skeleton keys.
We can drop the first wall, cast a Mage Hand into the middle area and then have it work the lever.
Did we try moving lever one up and lever two down "simultaneous"?
The DM (

) said we searched the first room
up to the first wall, not beyond it.
I'm still afraid that we can "break" this trap by using the mage hand.
We did try the simultaneous option. The end result was that acid sprayed out and burned me
for the forth time! (I still tried it once more after that)
I agree with the skeleton keys being our best option, and with the negative opinion of the DM

.