Ok, so i can press multiple claims.... how? I'm now officially the king of Scotland (usurped the title) and i want all the territories left (7) to be part of my kingdom. The territories are divided between two dukes, I would like to attack one and take everything he has at once (since its part of my kingdoms!), but i can only declare war for one county at a time.
You have to recognise there are different types of claim...
The de jure claim is what you are talking about, i.e. I'm the King of Scotland, that is part of Scotland and thus it should be mine!
That is a one at a time thing. It is a relatively weak claim, but it is a persistant one. It would take 100 years of the province being held by a different Kingdom to loose your De Jure claim I think...
For personal claims (the ones that appear on the character sheet of your ruler) you can press multiple. Best way to get them is to have you Chancellor faking claims for them all and then pressing them all at once...
Note also, IIRC, when you win a De Jure claim, the current ruler becomes your vassal (not sure what happens if they were a Duke and that was their only personal demesne). In a personal claim the province becomes part of your demesne to keep or hand out...