Tommen just doesn't have a tendency towards violence. He should definitely have stood up to the sparrow when he took the queen, but Tommen didn't know what to do. The reality is he should have ordered the kings guard to cut down the sparrows men when they would not allow him to talk to the sparrow a couple of episodes ago.
Sansa was a bit disappointing, its like she didn't learn anything from littlefinger. Not that she really could have stood up to Ramsay but she could have tried the old " I am your wife not your whore, get reek out of here or else I will develop a permanent headache."