My father with Parkinson's (limited mobility) needs some help in the bathroom making sure everything is "stowed for take off" before returning to his seat. My mother will generally wait until he has finished in the bathroom before just "checking on" him before he walks out of the bathroom at home or in stores or restaurants.

They are planning on flying from MKE/ORD/MDW to IAH/HOU and have some flexibility of who and when they fly. The idea of a bathroom before the flight in a family bathroom is a given but we need to also be prepared for a mid flight need as well. Do any of you have suggestions of which airlines or plane configurations will work better for 2 in the WC?