Is there any difference in the behaviour of the different kingdoms rulers?

I have been unable to find anything in the scripts about kings having different personalities. And yet people do seem to find that kings behave in the same way and lords having different personalities is well established.

In terms of explaining the behavioural differences you ask about (feasts, diplomacy, allocating conquests, lord relations) and others, if we assume there isn't anything about different personalities in the code then we have to assume its all circumstantial i.e. kingdom size, military strength, lord relations, number of factions they're at war with etc. I am inclined to go with this option on the basis of a couple of things from my own experience:

1) Kings all respond the same when you release them when you've captured them after a battle. Based on lord's personalities this would suggest kings are all the same personality type.

2) As a vassal it seems possible to influence your king's behaviour. If you make the kingdom stronger then they're more likely to come out of their city and e.g. join a campaign.

Finally, in terms of if it changes in Floris I haven't noticed any difference in the behaviour of kings whilst playing Floris but that's just my own experience.