To project & join walls & retain any openings in the walls you need to follow these steps:
Split each wall somewhere between the start/end of the wall & the first/last opening in the wall (shown in image below) by selecting a wall & going to the Split Wall Tool.
Select the two smaller wall segments (i.e. B & 2 shown in image below), right-click on one of them & select ‘+ WALLS > + Wall Operations > Project & Join Walls’.
Select the origin wall & the new wall (e.g. A & B shown in image below), right-click on one of them & select ‘+ WALLS > + Wall Operations > Meld Walls’. Repeat for the other walls (i.e. 1 & 2 shown in image below).