heir takes his or her allotted share after the deceased’s debts have been settled and any law-ful bequests carried out, and each heir may then dispose of that share as he wishes. When your portion of the estate reaches you, you may use it however you like: if you wish, you may fund a Hajj on behalf of your mother or give charity for her from your own share.
As for the other heirs’ portions, they may not be touched without their permission. If all—or some—of them agree to give charity or to have Hajj performed for their mother from their respective shares, that is permissible. But anyone who is not content with that and does not grant permission must be given his full share; nothing may be taken from it for charity or for Hajj.
With regard to visiting graves, it is legislated for every day, not only for Fridays or the two Eid days. The prescribed visit is one undertaken to draw a lesson, take admonition, repent to Allah the Exalted, and remember death, as the Prophet ﷺ said: “Visit the graves, for they remind you of the Hereafter.” It is also intended to benefit the deceased by praying for them, seeking forgiveness for them, and asking Allah’s mercy upon them, for they are in need of the living’s supplications and forgiveness every day, not merely on Fridays or the days of Eid.
As for the claim that their souls return to them only on those two days, nothing authentic has been established from the Prophet ﷺ concerning that. Such matters pertain to the unseen, knowledge of which belongs solely to Allah the Exalted, and it is not permissible to speak about them without a sound proof from the Prophet ﷺ.