There were seven people on the plane in Inception: Cobb, Arthur, Saito, Ariadne, Eames, Yusuf and Robert Fischer. They all went into a road rage in the first level of the dream, and on the second level, leaving Yusuf behind, who was driving the van, and in charge of waking them back up to the first level, the rest entered the dream.
On the 3rd level, they were in a heavily guarded snow-covered hill-top compound, leaving Arthur behind in the second level. Five of them enter, namely, Cobb, Saito, Ariadne, Eames and Robert Fischer, where Saito and Fischer die and Cobb and Ariadne enter the fourth level to bring them back, leaving Eames in charge.
Ariadne finds and sends Fischer back. On the 3rd level of dream, after Fischer's revival, only two (Eames and Fischer) were left. Fischer enters in a room with his Father's deathbed who (the Father) is supposed to plant the idea. Who is the father supposed to be impersonated by? It can't be someone from the team since there was no one left to do that. Then who was the Father and how?