Does anyone know how many people there are per boarding group? At exactly 24 hours, I got our boarding passes and we got A36, A38, and A39 (yeah, not sure what happened to A37, but no one is getting between me and my kids). My dad got his passes seconds behind me and he is B3 and B4. For some reason, I thought there were 60 per group, but I can't imagine 20+ people got boarding passes in those few seconds.
Put one of your kids in the seat that you want your Dad to have and leave the middle seat open on your row until he gets there. There's no way that anyone in the A group is going to want that middle seat and then you can just move your kid over a seat to let your Dad have the aisle. Have fun!!