No guarantees with Southwest boarding, even if you are BS A1! That said, if you both pay for EBCI, you will most likely both get A group numbers and easily get a window-center or aisle-center combo with little drama. Even the center (leg room) exit seat(s) stay empty deep into the B group on many flights.

I'm A Preferred, my wife is my Companion, and we still pay for her EBCI to minimize the drama