What is the ruling of Islamic law regarding daughters resorting to the judiciary to obtain their right to inheritance, and their mother boycotting them to pressure them into accepting an unjust division, and do the daughters bear sin as a result of that?

It is not permissible for a mother to wrong her children by preventing them from their right to inheritance or by forcing them to relinquish it. Allah Almighty has given everyone their due right, and she sins by wronging them. The heirs do not sin if they take the case to court, nor is this considered disobedience to parents. A Companion and his son sought judgment from the Prophet, peace be upon him, and he did not consider it disobedience. Therefore, resorting to the judiciary to obtain one's rights is not considered disobedience to parents nor a severing of family ties.