It's my understanding that Charles II's illegitimate children were not a close-knit group, probably because their mothers were rivals. Very little has been written about any of them besides Monmouth. Most of Charles II's biographers think the children were a pretty poor lot.
Perhaps because of the execution of Monmouth, it seems that all of Charles's children sided with William of Orange against James II. The Duke of Grafton was one of the first to desert James for William, and later died at the battle of the Boyne.