Is the remaining money with the deceased's sister her right, based on her brother's will for her to take it for her children before his death, knowing that his heirs will inherit his company?

If your brother gave you money that remained with him during his lifetime and not during his death illness, then this is a valid gift (hiba). However, if it was by way of a will (wasiyya) after his death, then if the amount was one-third of the estate or less, there is no objection to it. If it exceeded one-third, then the consent of the remaining heirs is required for the excess, unless the brother is not an heir due to the deceased having children. If the brother is an heir, then a will in his favor is not valid unless the remaining heirs agree to it. A gift given during a death illness takes the ruling of a will.