EDIT.
For the question regarding english kings.
The best solution would be: William de Normandie (since they used french language)
and creating a character in the family line, with the name Plantagenet.
Plantagenet should inherit he crown by some trigger, gameplay mechanics, etc. Only problem is it is not possible currently. So...We should
1,either accept the possibility that it is an altered history and the Norman dynasty may never die out, or if it dies out not necessarily Plantagenets inherit England.
2, or name (very unhistorically) William as Plantagenet
3, or as a third possibility use 'Of England' as a dynastical name, uniting the two dynasties.