Ujauja was torn, one the one side. Surviving was important and going home with these two was interesting. Somehow they had some sort of vested interest in him and it wasn't to kill him.
On the other hand, there was that vagrant soul chick, who carried a ridiculous amount of reiatsu and was thus very tasty. He desperately wanted to see her suffer.

Either way, as long as the shield remained it wasn't his decision to make. So he kept quiet and waited.