All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
You underlined that a son gets double the share of a daughter of the inheritance because he is financially responsible for providing for his parents or (unmarried) sisters; however, this is untrue. Some scholars highlighted that the wisdom behind giving the son double the share of the daughter with regard to inheritance is to establish justice in the distribution of duties and burdens according to the Islamic Fiqh maxim that reads, “privilege and loss go together.” Verily, men's financial obligations according to the Islamic Sharee'ah are substantially greater than women's financial responsibilities. These obligations are not specifically confined to the son's duty to provide for his parents and (unmarried) sisters. In fact, the Muslim man is required to pay Mahr to his wife, provide for his family, pay household expenses, pay his children's education expenses, buy them clothing, pay for their medical care and so on. On the contrary, the woman usually gets married and is not required to pay Mahr or provide for her family. Instead, her husband is obliged to provide for her.
The fact that you are financially supporting your parents is not a valid justification for you to get a larger share of your father's inheritance than that prescribed for you by the Sharee'ah. You will be generously rewarded by Allaah for providing for your parents or sister, because it is an act that indicates dutifulness and maintaining ties of kinship. Verily, this is a greater gain than any share of an inheritance or any fleeting worldly attainment. So, seek the reward of Allaah and dispense with any worldly gains in exchange for it.
You have stated that you and your father bought a bigger house for the family together. If you mean that you had helped your father financially and had given him money as a gift and not a co-ownership, the whole house is included in the father’s estate and you are entitled only to your share of it as per the Sharee'ah. However, if you had contributed with a share of the house’s cost, you are entitled to your share and it should not be included in the estate. In this case only the father’s share of the house is included in the estate. For instance, if you had paid half of the house’s cost and your father had paid the other half, only the father’s half is to be included in the estate and it should be divided among the eligible heirs, including you.
If the deceased did not leave any other heirs entitled to inherit other than those mentioned in the question, the wife gets one-eighth of the estate because the deceased has descendants entitled to inherit. Allaah, The Exalted, says (what means): {… But if you leave a child, then for them is an eighth of what you leave, after any bequest you [may have] made or debt…} [Quran 4:12]
The remainder of the estate is to be divided among the deceased’s son and two daughters by virtue of Ta‘seeb (i.e. by virtue of having a paternal relation with the deceased and not having an allotted share in the estate), with the male getting double the share of the female. Allaah, The Exalted, says (what means): {Allaah instructs you concerning your children: for the male, what is equal to the share of two females…} [Quran 4:11]
Hence, the estate should be divided into thirty two shares; the wife gets her one-eighth, i.e. four shares, the son gets fourteen shares, and each daughter gets seven shares.
Allaah Knows best.