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.
It is not permissible to prevent you from the inheritance because you are married; indeed, a daughter inherits from her father whether she is married, or virgin, or divorced, or else. Marriage is not one of the impediments that prevent an heir from inheritance. The impediments of inheritance are three: killing, slavery, and the difference of religion.
Also, it is not permissible for the wife of the deceased to appropriate part of the inheritance to the exclusion of the rest of the heirs; rather, she should take only her legitimate share which is one-eighth of the inheritance.
Dear Sister, what we can say to you is that if the heirs refuse to give you your right in the inheritance, then you may take the matter to an Islamic court so that the latter would give you your right, as Allaah may prevent someone from doing evil by the ruler if He does not prevent him by the Quran (i.e. He deters with the ruler whom the Quran cannot deter). Of course, taking the case to the court is not considered as undutifulness to your mother.
As regards what you mentioned about your father that he had written a will, then if you mean that he had made a will for any heir, then making a will for an heir is Islamically forbidden and such a will is not effective unless all the remaining heirs approve of it as the Prophet said: “Allaah has given everyone who has right what is due to him, so there is no will for an heir.” [Ahmad, At-Tirmithi, Abu Daawood, An-Nasaa'i and Ibn Maajah]
If the deceased did not leave any other heirs except those mentioned in the question, then the wife gets one-eighth of the inheritance as her legal share due to the existence of the children (of the deceased); Allaah Says (what means): {But if you leave a child, then for them [i.e. the wives] is an eighth of what you leave, after any bequest you [may have] made or debt.}[Quran 4:12]
The remainder should be divided amongst the son and the daughters by Ta’seeb (by virtue of having a paternal relation with the deceased); the male twice the share of the female as Allaah Says (what means): {Allaah instructs you concerning your children [i.e. their portions of inheritance]: for the male, what is equal to the share of two females.}[Quran 4:11]
Therefore, the inheritance should be divided into 40 shares, the wife gets one-eighth, which is 5 shares, the son gets 14 shares, and each daughter gets 7 shares.
Allaah Knows best.