There is a very interesting article on wikipedia on Welsh Law. Though it defines the structure of the Court in Wales in the late medieval period, it says nothing of the status of other nobles and notable personages compared to those in the king's household.
In addition to that I read that both Ireland and Wales consisted (pre-Normanisation) of petty kingdoms. What was the way these kingdoms worked? Did they have a common social structure and laws? Were they classic fiefdoms with the king appointing the power to the Nobles and they in turn to other minor ones? Was there a reason why these two nations have so much in common (common ancestry maybe?) or is it far-fetched to even propose that. Even their laws seem to have been of the same philosophy.