How can one dispose of the money and belongings of a deceased sister, knowing that she bequeathed them to only one of her sisters and her children, excluding the rest of the heirs whom the deceased sister believed had neglected her? And is it permissible to give charity from her money after her severe illness and before her death?

The deceased's bequest to you of gold and money is a bequest to an heir and is not enforceable unless the rest of the heirs agree to it. You must inform them of this. As for the charity you gave, if it was at her instruction, then it is valid. If it was without her instruction, then you are liable for it to the estate, and you will have the reward for the charity. This is because the validity of charity requires that the giver of charity be the owner of the money or an agent on their behalf, and it is not valid without the owner's permission.