My advice, keep all three tickets on the same PNR, that way with your status you should be able to select seats when contacting AA. I have plt status with AA and have used it to preselect seats when flying on IB, I had called IB directly and the agent made the seat selection for me. I've also been able to make seat assignments for one travel companion on the same PNR. I suggest you call AA to ask for a seat assisignment.