Hello
the best thing to do is check in at the 24 hour mark before the flight using the confirmation number and usually it will give you numbers in order like A50-60 or B3-29 as a couple examples sometimes people may get split based on other checking in at the same time but usually you will be together since you will be on one confirmation number. Usually I would recommend EB check in for groups but since you did book through southwest group reservations you can't add EB check in. So as long as you check in at the 24 hour mark you should be able to get a good set of boarding number for seats near each other now you may not all be together you should be able to get several rows towards the back but there are no assigned seats. It's also possible that some may get A boarding while others get B just tell those with A to save some seats.
Hope this helps
Blake
