Ram(R) and Laxman(L) go first. Total Time = 2 minutes

R comes back. Total Time = 1 minute

Bharat (B) and Shatrughan (S) go with the torch. Total time = 10 minutes

L comes back with the torch. Total time = 2 minutes

R and L go to meet B and S on the other side of the tunnel. Total time= 2 minutes

Total time taken for all this = 17 minutes.