I am intending to cut out two egress windows in the side of my house. Instead of digging 2 holes, I was hoping to dig one and cut both egress windows within the same well. The well will be built with 4x6x12 timbers (3x12 window well), with 2 48x48 windows. There will be 20" of concrete between the two windows. I am struggling to find anyone doing this, so I am wondering if there is a problem with my plan. Thanks much!
I don't see a problem with this. Use PT wood treated for continuous underground use. (Wood foundation treatment) You're using heavy timbers to the ground forces trying to squeeze in won't be an issue. You may get minor amounts of water squeezing between the boards, but with reasonable bottom drainage this isn't aproblem.
The reason the galvanized corrugated wells are used are a matter of cost. They are cheap, and quick to put in.
Be sure that your well goes down below the window, then fill back with fast draining rock to a couple inches below the window sill.
Also try to anticipate things going wrong. A well can act as a funnel, moving water from the yard into the the house. Mis-set sprinklers, clogged eavestrough, snow sliding off a metal roof....
I have seen people who propped old windows over the window well. This still allowed it to be used as an egress, but prevented most of the misshaps. One person did a tiny shade garden in the window well. It would get trampled in an emergency exit, but what the heck?