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 is His slave and Messenger.
First of all, before dividing the estate among the heirs, the due Zakah that the deceased did not pay must be deducted from the estate, because the Zakah is a debt that should be given to its rightful recipients and it should not be included in the estate.
In addition, all the debts of the deceased must be deducted as well before dividing the estate because the right of the creditors is given priority over that of the heirs in the estate. Ar-Rawdh Al-Murbi‘ reads, “It is incumbent on the guardian (and if there is no guardian) then on heir (and if there is no heir) then on the ruler, to deduct all the liabilities from the deceased’s estate such as debts, obligatory Hajj expenses, and the like as well as the Zakah, vows, and expiation from the overall estate even if the deceased did not mention it in his will. This is because Allaah, The Exalted, says (what means): {… after any bequest he [may have] made or debt...}[Quran 4:11] Moreover, ‘Ali said, "The Prophet judged that debts are to be paid before the will (is executed)...” [At-Tirmithi]
After the deduction of all the due debts and liabilities, the remainder of the estate is to be divided among the eligible heirs. If the deceased did not leave any eligible heirs except his son and two daughters, then the remainder of the estate is divided among them by Ta‘seeb (i.e. by virtue of having a paternal relation with the deceased and not having an allotted share in the estate); the male gets twice 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] So, it is divided into four shares; the son gets two shares and each daughter gets one share.
As for your question about a verse stating that a disbeliever does not inherit a Muslim, there is no verse that explicitly states that. However, the Quran enjoins Muslims to obey the Prophet and he said: “A Muslim does not inherit from a disbeliever, and a disbeliever does not inherit from a Muslim.” [Al-Bukhari and Muslim] The prohibition of inheritance between a Muslim and a non-Muslim was stated in the Sunnah, which is a source of legislation just like the Quran. A Muslim should know that Allaah revealed to the Prophet the Quran and the wisdom. Allaah, The Exalted, says (what means):
{… And Allaah has revealed to you the Book and wisdom and has taught you that which you did not know...}[Quran 4:113] The Prophet taught the Companions this wisdom just as he taught them the Quran; Allaah says (what means): {… and teaching them the Book and wisdom ...}[Quran 62:2]
Shaykhul-Islam Ibn Taymiyyah wrote, “Allaah, The Exalted, revealed the Quran and wisdom, reminded the believers of that blessing, and commanded the wives of His Prophet to remember it; Allaah says (what means):
• {… And Allaah has revealed to you the Book and wisdom and has taught you that which you did not know...}[Quran 4:113]
• {Certainly did Allaah confer [great] favor upon the believers when He sent among them a Messenger from themselves, reciting to them His verses and purifying them and teaching them the Book and wisdom...}[Quran 3:164]
• {And remember what is recited in your houses of the verses of Allaah and wisdom. Indeed, Allaah is ever Subtle and Acquainted [with all things].}[Quran 33:34]
Many of the righteous predecessors said that the word "wisdom" in these verses refers to the Sunnah because what was circulated in the houses of the Prophet’s wives other than the Quran was his Sunnah. Therefore, the Prophet said: “I have been given the Quran and what is like it with it …” Hassaan ibn ‘Atiyyah said, “Jibreel (Gabriel) used to descend upon the Prophet with the Sunnah just as he used to descend with the Quran, so he would teach him Sunnah just as he taught him the Quran.” [Majmoo‘ Al-Fataawa]
Please to Fatwa 189195 about the different opinions of the scholars of Fiqh regarding the inheritance of the Muslim from the estate of the non-belligerent disbeliever (who does not fight Muslims).
Allaah Knows best.