The Imams’ attitude was covered in Halil Inalcik’s book The Ottoman Empire: The Classical Age.

The background was that the Ottoman state never had a tradition that the eldest son was by default the only legally valid successor.

Instead the idea was that the most powerful son would take over. This led to civil war with massive death at every succession.

The Imams were needed to legitimize the execution of Sultans’ siblings. They were were brought onboard because in Islamic law there is a principle that an evil can be made permissible to avoid a greater evil.

In this case, if the murder of the sultan’s siblings would prevent civil wars where thousands or tens of thousands of citizens would die, then the murders were the lesser of the evils and would be allowed.

The Imams thus backed this succession practice as an exceptional circumstance.