I dont get what your asking. If u explaint to me what your asking ill tell you the answer in the comments.
The total resistance is 5000 N. So the net force left for acceleration is 7 000 N (12 000 - 5 000).
7000 N applied to 2x700 kg gives a maximum acceleration of
a = F/m = 7000/1400kg = 5 m/s^2
At 5m/s^2, it will take 8 s to reach 40 m/s. In 8 second the distance covered will be
d = 1/2 at^2 = 1/2 x 5 x 8^2 = 160 m
Because each glider has the same drag and inertia, the tension in the rope between the gliders will be exactly half of the tension between plane and the two gliders:
12 000/2 = 6 000N.