Is it religiously correct for a father to favor his youngest daughter in giving (building a house for her first), while delaying giving to his eldest daughter, even though he is well-off and there is no reason for this favoritism?

A father should treat all his children equally in all matters, including emotional treatment and gifts. It is permissible for a father to give one of his children something with the intention of balancing it out in the future. If there is no justification for favoring the youngest, then it is preferable to favor the eldest, in accordance with the Sunnah regarding imamate and prioritizing the elder in some other Islamic matters. If a daughter perceives favoritism from her father, she should advise him gently and beware of disobedience to parents.