I have a 922 sq. foot 2 story townhome built in 1973. It has no ducts for a/c. Thinking of putting in two encased wall units, 12,000 BTU's. One for ground level, the other for the small master bedroom, plan to leave door open to circulate to other bedroom and small hallway. Should I go smaller on 2nd floor? The other option is to install two small 110 units instead. The top floor get SUPER hot, even in September! Attic not insulated well.

"the other for the small master bedroom, plan to leave door open to circulate to other bedroom and small hallway". Not logical solution. 12,000 BTU in a bedroom is too much, you will freeze in the summer and will not distribute to the other rooms. First priority is insulation, otherwise you will be wasting money. You would be better off getting 6-8,000 BTU for each BR, larger for first floor