I think you can probably expect the chickens to harass them some. But it all depends on the personality of the chickens. Right now I have some 9 week old guineas that I am starting to integrate into the flock. For the last week or two I have put one or two chickens in with my two little guineas and leave them together for a while. Some hens will ignore the little ones and get along just fine.. Some of the hens will act aggressively to the guineas so they are removed pretty quick. This evening I added a rooster and two hens to the cage where the guineas sleep. No problems at all.
It wouldn't hurt for your guineas to be a little bigger before exposing them to the entire flock of chickens. But you could start now by adding a couple of your more docile chickens to the pen that the guineas have. I think integrating gradually is the best approach.