Saxon Kingship differs from the more familiar later Feudal set up which is most often seen in RPGs. Early Saxon kingships, wasn’t hereditary and wasn’t permanent. Kings were chosen by their peers, and ruled only as long as their kingship was deemed successful, which invariably meant successful in war. A king considered unskilled or even unlucky in war would be replaced.
Another noticeable difference is the concept of dual kingship. Kingdoms were often divided into two, with a king ruling each half of the kingdom, but nominally ruling the whole kingdom together. Very often these dual kings would be related, father and son, brothers, cousins, etc. This would cut down on rivalry (a little). Another common practice would be to pair a young king, with an older king; the older king guiding and advising the younger. This provided a certain amount of continuity when the younger king eventually became the senior king in a new partnership.
There is one other element of early Saxon kingship that is the most important in the context of Redwald, and that’s the fact that the assassination of kings seemed to be a national sport.
Seriously if you were in the kingly burial mound business you’d have plenty of work. A usurper would barely have the knife out of his predecessor's back, the crown on his head, and his arse on his throne before he’d be fending off the first attempt on his own life. Plenty of work for the player characters in other words.