How can I deal with my fiancé's family—including his mother, father, and brothers—when living with them in the same house, knowing that I wear a niqab and do not wish to be a servant to them, but rather desire to please Allah in my actions, given my fears about my mother-in-law's neglect and its impact on our shared life and my fiancé's prayers?

You must avoid attending gatherings of sin, for whoever does not avoid them has condoned their actions. As for dealing with the husband's family, it should be done with kindness, and the mother-in-law should be treated like a mother. Avoid backbiting about her or describing her in a way that displeases her. The father-in-law must be shown respect, and one should act in a good manner, while being careful not to mix with the husband's brothers or be in seclusion with any of them. Serving the husband's family is not an obligation according to Sharia, but doing so for the sake of reward and to please the husband is commendable. Visits to them should be reduced to avoid the harms of mixing, while ensuring that these visits are for a beneficial purpose. As for the suitor, it is recommended to perform Salatul-Istikhara and verify his religiosity and character before finalizing the contract.