How to mount multiple mirrors on a wall
If you've ever watch a pro install mirror walls, they have a bucket of construction adhesive, made for mirrors, and they put a glob on each corner of the mirror and a glob in the center. They then place it on the wall and push. They will stick even if the wall isn't smooth and they can be adjusted if the wall is uneven. You'll need to support the bottom row with clips or a 1x2 fastened to the wall.