All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
According to the consensus of scholars, it is required of the father to establish justice among his children when offering them gifts. The Prophet, sallallahu ‘alayhi wa sallam, said, "Fear Allah and observe justice among your children." [Al-Bukhari and Muslim] The majority of the scholars held that it is recommended for the father to give his children equal gifts, and that it is not obligatory. The Hanbalis, on the other hand, held that it is obligatory and that it is prohibited for him to favor some over the others with gifts for no valid reason.
The scholars held different views as well regarding how to establish justice between male and female children in giving gifts; are they to be given equal gifts or are males given twice the share of females? The famous view of the Hanbalis is that males get twice the share of females.
In any case, the majority of the scholars - except for a few - held that if the father gave his children a gift and did not observe justice and equality among them and then passed away before taking the gift back, the gift is binding and they are not obliged to give it back - if it fulfills the rest of the conditions of a gift. The rest of the children have no right to demand any share in the gift, even according to the preponderant view of the Hanbalis, who held that the parent is obliged to establish justice among his children when offering them gifts.
Ibn Qudaamah wrote, "If the father favors some of his children over the others in terms of gift giving or gives some and denies the others and passed away before taking back such gifts, then the beneficiaries of the gifts are entitled to keep them, and the rest of the heirs have no right to revoke the gifts. This is the view narrated on the authority of (Imaam) Ahmad. It is also the view of Maalik, Ash-Shaafi‘i, the Hanafis, and most of the scholars..." [Al-Mughni]
Hence, you should know that the general majority of the scholars held that you are not obliged to return the gifts to the estate, even if you were favored with them without a valid reason. If you willingly choose to return what you were favored with to the estate for the sake of your sisters, then that is more prudent in terms of clearing yourself of your liability and better for fostering the ties of kinship and removing traces of jealousy from the hearts.
Allah knows best.