When I have flown on SW, I have always had an A boarding group. But, with the preboarders getting there first, it made it difficult for my dd and I to find a middle/window seat combination until we got back past the wing.
I remember that the B's boarding later were able to get seats together, but towards the rear of the plane. But, I can't say what their seating situations were...I just remember that no one seemed to be put out. You may have to split up..two and two, but that shouldn't be an issue. I don't think you'll have to sit singly though.
The other thing to remember is that with the changes to SW boarding, it will make a difference what number within the boarding group you have....someone holding a B3 pass, with the others in his group holding B4, B5, and B6, will most likely be able to find three across and one on the aisle. But...if they had a B24, B25, B26, B27..the chances would diminish greatly. So it would behoove people to get on line as soon as humanly possible. But, I don't think those changes are coming until early November.