Havent time to read all replies, but an (older?) child of the deceased William had died previously, and left orphan children. William had guaranteed that the goods value would be paid to the orphans when they came of age. He failed to set the money aside, and on death his net personal property diud not cover the orphans' missing money.
Agree with Frances highly likely that Thomas Skillicorn is the stepfather to the orphans. Hard to say if the orphan's father was the heir, but study of the composition book might be worthwhile. The Phill Kissag could provide a clue to the location of the family, I think he may be from Onchan, around Hilberry??

NGC