Is it permissible to restrict business assets and allocate one-sixth of the amount, depositing it into a bank account in the name of the grandmother, who is around 100 years old and not fully aware of matters, without closing the business, knowing that it is the family's source of income?

If the heirs are limited to the wife, the mother, sons, and a daughter, then the mother gets one-sixth, and the wife gets one-eighth due to the presence of a lineal descendant heir. The remaining portion is distributed among the sons and the daughter by ta‘ṣīb (agnatic inheritance), with the male receiving the share of two females. The inheritance is divided into 168 shares.

As for your paternal grandmother, if she has lost her mental faculties, her case must be brought before the Sharia court to appoint someone to manage her wealth and dispose of it in a manner that serves her best interest. The questioner is advised not to distribute inheritances without consulting the Sharia courts.