The deceased had formed a trust. His heirs are therefore unable to take possession of their shares of the assets.

Answer

The trust mentioned by you has no validity in Islam. When a person dies, his heirs automatically become the owners of their respective shares in the estate of the deceased. It is haraam to contrive any scheme such as a trust, etc. to deprive or prevent the heirs from taking immediate possession of their Shar'i shares of inheritance. It is Waajib on the executors to dissolve the haraam trust and to finalize the distribution of the mayyit's estate. If the executors/trustees refuse to dissolve the trust despite this being possible, they will be major violaters of the Shariah. Their sin is excessively grave for they are guilty of usurping and denying the heirs the rights which the Shariah has ordered for them. The Qur'aan warnas of the Fire of Jahannum for such violaters of the Shariah.