Will the sisters be sinful if they refuse to redistribute the inheritance according to Islamic law, claiming that the Islamic distribution is unjust, and insist on adhering to the European country's law which stipulates equality? And will their right remain a liability upon them if the brother does not forgive them?

The law does not make lawful what is unlawful, nor does it make unlawful what is lawful, nor does it permit taking more than one's legitimate share of inheritance. The sisters must fear Allah and be content with the lawful division, because their saying that the lawful division is unjust is disbelief; for judging by systems that contradict the Sacred Law is disbelief, and the Sacred Law decreed by Allah allows no room for ijtihad (independent reasoning) and does not change with the changing of times.

They must repent to Allah; for a single dip in Hell will make the most blessed people in this world forget all their blessings. If you are unable to claim your lawful right, it will remain their responsibility, and you will take it from their good deeds on the Day of Judgment, or some of your sins will be cast upon them.