Alternative solution: give your brother ear plugs for the duration of his visit.
A pole with a thick curtain can muffle the sounds somewhat, but not much and the curtains needs to be very thick and heavy. All the sounds that are transmitted through the ceiling/floor (any walking around, opening and closing doors, creaking floorboards, moving objects over the ...
Most knob sets with that hole on the outside are intended to be unlocked with a small flat-blade screwdriver. Some come with a "key" that is just exactly, made from bent heavy wire.
Try shining a light into the hole, you should see a slot inside; put a small screwdriver into the slot, and turn one way or the other. Done!
As with all wooden items, they should be stored flat with gaps all round for air flow to prevent warping. Propping against a wall will encourage warp as the wood soaks the moisture from the air and nothing supporting the middle from sagging.
Look at the storage section of https://www.intouch-quality.com/blog/wood-warping-and-how-to-prevent-it