Sanballat continues his derision with asking, Will they restore it for themselves?
The words for themselves
prompt us to think that Sanballat is criticizing the goal of the project, namely, that the Jews would rebuild for their own benefit. We would do better to understand Sanballat as saying, Will they restore it by themselves?
That formulation flows directly from the first question. It is meant to convey that the project is way beyond their (feeble) abilities.
2 And he said in the presence of his brothers and of the army of Samaria, “What are these feeble Jews doing? Will they restore it for themselves? Will they sacrifice? Will they finish up in a day? Will they revive the stones out of the heaps of rubbish, and burned ones at that?”