Is marriage to a divorcee who is 14 years my senior and has a child, conducted by a sheikh with a legitimate contract, permissible or forbidden, with my family's knowledge and her family's ignorance?

The majority of scholars consider marriage without a guardian (wali) invalid, while Abu Hanifa deems it valid. Therefore, your marriage to the woman without her guardian's knowledge is invalid according to the majority and valid according to Abu Hanifa, provided the other pillars (arkān) are met. The preponderant opinion is that of the majority of scholars, and accordingly, the contract must be renewed in the presence of the woman's guardian. Children born before the renewal are attributed to the husband.