Will the husband be sinful for helping his sisters study in a European country, when they go out without a mahram, and live with him and his wife despite her objection, and can he please his parents and his wife at the same time?

A wife has the right to a separate dwelling, and her husband is not permitted to house anyone else with her except with her consent. She has the right to refuse if she does not agree. Residing in non-Muslim lands is not permissible except out of necessity or dire need, such as studying a field of knowledge that Muslims require and which cannot be studied elsewhere. For a woman, the presence of a mahram is a prerequisite. A woman's movement within a city, without undertaking a journey, does not require a mahram, provided there is safety. The wife should inform her husband of these rulings and agree with him gently and kindly.