What should I do about my family's refusal of my marriage to a girl of good character and faith, on the pretext that her family's dwelling is unsuitable for my family, and should I leave the girl to please my family, or adhere to the principle of Islam?

You are not permitted to marry this girl if your parents object, because obeying them is obligatory, while marrying her is not. However, if they forbid you from marrying entirely, or if you fear falling into haram, then there is no obedience to them in that. We advise you to be patient and try to persuade them gently and wisely, for what Allah has chosen for you contains goodness.