Is a marriage conducted by proxy, with written permission, and in the presence of the husband, two witnesses, and the local imam, valid and permissible, despite the family's unawareness of the contract's completion?

First, your presence is not required for the marriage contract; your written permission suffices.

Second, your guardian (wali) or his representative must be present, as a marriage without a guardian is invalid, based on the Prophet Muhammad's (peace be upon him) sayings: "There is no marriage except with a guardian," and "Any woman who marries without the permission of her guardian, her marriage is invalid."

If your guardian was not present at the contract, then the contract is void and must be re-done with the presence of the guardian and two witnesses, unless your guardian is not Muslim. In that case, the Muslim judge or the director of the Islamic center would be your guardian.