If you are the originating city, you'll be fine. If this is the case...A1-15 slots are held for business select people. Then A16 on board. Then, SW usually allows families traveling with kids under 4 to board right after the A group (obviously the family has B or C slots!!). Then the Bs board, followed, finally, by the C group.
B10, 11, 12 and 13 aren't bad at all. You will most likely be able to get three of you seated together with the fourth behind, in front, or across the aisle from you.
If you are on a flight that originated someplace else? It will be a bit harder. Some passengers will most likely get off. So that will empty up some slots. But you may very well find it impossible to get three seats together. You may be able to get two people together though....times two.