monarchs.fri doesn't seem right. It starts with chieftains of Jever (Edo Wiemken and Hayo Harldas), then jumps to Wibet von Esens of the Esens, then to a rival family of Wittmunds with Tanne von Wittmund and then ends correctly with Sibet von Dornum and Hero Oomkens.
Although some earlier posts suggest that it has been agreed that Friesen represents West Frisia, Frieslands monarchs are all from East Frisia. I think we should choose one family and stick with their monarchs for Friesland.
This page:
http://www.tacitus.nu/historical-atlas/regents/benelux/frisia.htm has a list of rulers of Jever. They are the House of Wimkrok.
If we opt for the union of Esens and Wittmunds, this page has some info:
http://harlingen1.tripod.com/id3.html . Since the two families were united by a third family that ruled the declining city of Stedesdorf, I think their line should be used if we choose this option. It should be:
Hero Oomkens the Elder (-1440) (married into Esens)
Sibet von Dornum (1440-1473) (conquered Wittmund married Onna Oomkens)
Hero Oomkens the Younger (1473-1522)
Balthasar Oomkens von Esens (1522-1540)
If necessary, the line can be extended by Balthasar's sister, Onna Oomkens or her husband, Otto von Rietber (1540-1560)
In my humble opinion, if eastern families are used, we should use the Cirksena from the first link I provided. Friesland is a part of HRE in the game and Cirksena were made counts of the Empire. Their line is also the longest, providing monarchs for Friesland should it survive too long (until 1744).