Ijaarah

Q: If a person is working in a non mixed environment, all his needs are being met. Is it permissible for him to take a job in a office where there is both genders working freely and he will have to communicate with the opposite gender, in the name of progress?

Also a person is working in a Islamic school and is married. It is a fully segregated environment. He earns less but through other jobs like picking up and dropping of kids he covers everything else. This person studied in college and studied other certifications and worked in an office environment with non-Muslims for over 5 years. He left it due to getting the opportunity to work in a halal environment. Now his father keeps telling him you are stupid for leaving and you should stick to your career. A Muslim must be strong and not weak, he should go into there environment succeed and give dawah. But this person refuses and stays content with the Islamic school job. Is this person doing something wrong by not listening to his father? The reason why I am asking is because in this time it is so confusing even when you try to save yourself from sins, parents and relatives say that we are narrow minded even though that said parent may have went 4 months jamat 5 times and reads Moulana Ashraf Ali Thanvis books.

Also, this parent listens to other scholars that say that if a person is living in the west and doesn't get to study there, schooling is at a loss. Im so confused. Is it permissible for a person to commit sin and earn a little bit more halal earning, like lying on a resume working with non-Muslims. Is this person that works at the Islamic school stupid for not wanting to go back to his career and is he selling himself short. The person still has ambition and inshaAllah if Allah gives him the chance he will try and work on some business. But he doesn't want to go back to the haram career.