Hi- all guineas are different .When I gave my GP1 and GP2 coriander it was probably too much and it co-incided with them coming in for winter. (Smaller cage, more noise indoors, being forced to stare at each other all night ) But they went ballistic, our very gentle GP2 climbed onto GP1 from the side and went for him (unlike GP3 who tries to bonk him from the backend but no violence just a look from GP1 you're on the wrong boat there, sonny. :/
I gave them a couple of sprigs when I made salsa (they didn't eat the mint. They don't like basil)
Maybe just a couple of sprigs and watch their antics. Ir sounds like it turns your guineas mad in a good way
(the only damage is it's relatively high in calcium, so a couple of sprigs as a treat. GP1 idea of a couple of sprigs isn't mine)
Ours have had it a couple of times (it was about half a bag the first time ) - we only give it to them when they're out in the run with a couple of boxes/tubes to play with. They generally run round like nutters popcorning and chasing each other for about 20 minutes, than flake out together in a furry heap looking extremely cute and pleased with themselves .