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. We ask Allaah to exalt his mention as well as that of his family and all his companions.
The will of the deceased to his daughter cannot be fulfilled unless the other heirs permit it as the Prophet said: "Allaah has given everyone his right, so there is no will for an heir." [Ibn Maajah, Abu Daawood and others] His daughter is among the heirs. As regards his will that they should perform Hajj on his father, mother and grandfather with the mentioned amount of money, then this will has to be fulfilled as it is permissible for a person to make a will of less than a third of the inheritance for charitable purposes. The Prophet said regarding the portion of will: "Make a will in one-third (of your property), and one-third is too much [i.e. the will must not exceed one-third of the whole property]". [Al-Bukhari and Muslim]
The amount that your deceased father has specified in the will is below one-third of the inheritance so it has to be fulfilled according to his conditions without any change. Therefore, it is not permissible to go against his will, and whoever alters it, or changes anything in it, and does not fulfil it, is sinful.
Allaah Knows best.