Is it permissible to feed non-needy relatives from a vow sacrifice, or to bring a portion of it into the house, knowing that neither the one who made the vow nor his relatives are needy?

Undertaking a vow (nadhr) is disliked. However, if one vows an act of obedience to Allah, then fulfilling it becomes obligatory. If you intend to direct the vow to the poor, then it is not permissible for your wealthy relatives, nor you, nor anyone from your household to eat from it. However, if you did not intend to direct the vow to a specific party, then it is permissible for you and your wealthy relatives to eat from it according to some scholars, but it is better to avoid that.