What is the ruling on forging documents to invalidate a will for an heir if it is the only means available before un-Islamic courts?

A bequest to an heir is legally prohibited and does not take effect except with the consent of the other heirs. If the heirs know that it will be enforced upon them by compulsion and they find no means to invalidate it and remove the injustice except through forgery, then there is no blame upon them for it, provided they are safe from its consequences, meaning that its matter is not exposed and no harm results from it.