"What you see" would be what Terrel and Chekov can see in the containers. We can't see everything they see; there's quite a lot of ground to cover behind the camera's point of view, even assuming there are only those two containers and not a third one they didn't get a chance to see.But (according to Khan) what you see is all that remains, certainly not "53."
But even excepting that, Khan isn't exactly giving them an inventory here. He's making a big dramatic speech to the two people he's just captured: he's not going to say "What you see, in addition to fourteen others on the south ridge, plus the hunting team seventeen kilometers due south who are gathering meat for this evening's supper, and lest I forget those two assholes I put on latrine duty around the corner..."
The best we can say is that there are at least fourteen of them. Possibly more, possibly less.
IIRC, Khan pronounces his name differently in Space Seed than he does in TWOK. Differently enough that it would be consistent with them not being played by the same actors since they are not actually the same person.Sure we saw him in Space Seed, he was referred to by name
Either way, though, it stands to reason that Khan had considerably more than fourteen people in his crew when he took over Reliant; he apparently couldn't run the Enterprise with 72 unless he got a couple of the Enterprise crew to help him. Reliant may have been easier, but not THAT much easier.