Conflicting claims -- anyway to circumvent?

[DeaTh-ShiNoBi]

I neighbor the Grand Principality of Kiev, and mismanagement and inheritance issues have left them a hollow shell of their former power, and I want to press my "weak claim on Kiev" in war, which I would win handily. However, I have several vassals that also have a "weak claim on Kiev", and for some reason the declare war menu seems to only allow me to wage war for the sake of my vassal (screw that, obviously, I wouldn't even get to rule them since I'm not a King).

Incidentally, this is not even the first time in my game that this has happened to me. Quite a long time ago, Novgorod absorbed Kiev, and since the former Grand Duke of Kiev was my half-brother, he came to my court. In the declare war menu, I could only wage war for his sake (we both had strong claims at the time). Is there any way to fix this issue?

Edit: problem solved; it wasn't a conflict of claims or a bug, it was simply a feature of Project Balance. See below (third post) for details.

 

[DeaTh-ShiNoBi]

Update: I used my chancellor to forge a strong claim on the county of Kiev and I STILL cannot press it in war. Somehow the weak claim that my vassal has (which, incidentally, I have too) on the duchy of Kiev overrides the option for me to press for the county of Kiev. I even wasted 100 prestige and 250 gold on that apparently useless claim. What do I have to do? Murder all my vassals that have claims on Kiev to take it? This is ridiculous. What a stupid bug.

 

[DeaTh-ShiNoBi]

Second Update: I now believe I know the reason why I could not declare war for myself. It's not a bug, it's just a feature of Project Balance (which I'm using), where you can't declare war on allies (except excommunication) unless you have certain traits (ambitious, lunatic, etc.). The part that confused me (and still kind of does...) is that I could declare war for the sake of my vassals, despite the restriction. My first ruler could freely declare war on allies to press claims that he had. Of course, now I see that he was ambitious, but my next rulers didn't. So it's not a bug; problem solved.