The File:
The investigation of the Stormmoon household proved fruitless. First, given the size of the mansion and the wealth of the family, the staff was very small; only four comprised of a groundskeeper, chef, cleaner and secretary. Second, the decedent dismissed the staff during his period of seclusion and had not yet hired them back at the time of the murder. Fortunately the staff members were easy to locate as the Stormmoon children had hired them to their own homes while they attempted to convince their father to rehire them.
The staff confirmed what was already well known: Abram Stormmoon was crushed by his wife's death, withdrew from his family and friends, becoming increasingly distant and isolated until late 782 when he appeared to make a recovery. By all accounts he had always been an independent man, hence the small staff, and was dedicated to his family, his city and the Kingdom.
I don't believe his family played any part in this murder. This was an assassination; his work on the Council, his business or some other interest is the motive for this crime.