Is it considered disobedience to one's father, who rejects his daughter-in-law's return, if the husband takes back his wife after divorcing her due to conversations with foreign men, and what should the husband do in this situation?

Obeying one's parents is obligatory in matters that benefit them and do not harm the child. If the rectitude of your divorced wife becomes clear to you, and you are able to act justly between the two wives, and there is no justification for your father preventing her return, then there is no objection to taking her back, even if your father does not approve, especially if there is a fear of harm to your children. Strive to convince your father, supplicate to Allah, and seek help from some virtuous people. If she is still within her 'iddah (waiting period), it is permissible to take her back without a new contract. If her 'iddah has ended, then it is not permissible to take her back except with a new contract.