The higher ranked of those teams is likely to go to the Rose Bowl. I think it will be OSU. If I'm right, then I think the likely matchups are ND-Houston in the Fiesta and FSU-Iowa in the Peach, although it could be ND-Iowa in the Firesta and FSU-Houston in the Peach.
If Iowa goes to the Rose, then I think they'll split ND and OSU for attendance and ratings purposes. I would expect ND-Houston in the Fiesta and OSU-FSU in the Peach.
If ND were to go to the Peach, the likely opponent would be FSU. I don't expect that to happen.