What's the best method to deal with a kd that is greifing your's, if they are are roughly 30% your size?

They unfortunately have one or two unbreakables (huge networths within a 4 prov kd to our 23) that are casting away (so we are running ops on them) but is the best bet to just ignore them and MV when they throw up duration spells, or to just slog it out with them over a few days and eventually completely annihilate them?

I feel a little bad, because I feel its a piss poor monarch they have that is bringing trouble down on the rest of them, so each attack or op we run against the rest of the folks in their kd (to keep their ability to op down) makes me sigh a little and feel a little bad for potentially ruining some other person's age. It feels like wasted time but like you cannot just sit there and let it occur.

Anyone else been griefed by a tiny kd like that?
What's the best approach, wait it out and ignore them, or just sink them?