I am the owner of an SMP, sometimes the nations can declare war on eachother, but for that to happen they need to be able to change these options, how do I do so and why are they grayed out? Thanks for advance

It's explained on the mod page. https://www.curseforge.com/minecraft/mc-mods/open-parties-and-claims

Should I use FTB Ranks or another perm mod to do so?

No. Did you read about the greyed out options on the mod page?

I couldn't do at the time I messaged you, I'm sorry, but I understood now how it's done, so thank you.