As for adults.. seems to be split between 'get along ok' and 'does NOT get along at all/got rid of the &%^%& guineas'.
Comments along the lines of getting rid/never getting guineas again are not uncommon due to the guineas doing something like constantly ganging up on roosters, all birds of a specific color, being relentlessly obsessive about keeping other species away from food/water.. can be one or more of above or other odd things.
I only have a pair.. the male does like to 'charge' at the chickens, especially roosters.. many roosters are extremely frightened of him(he does a body slamming thing if he can). He also for whatever reason suddenly gets obsessed with making the tom turkey move for an entire day.. if the turkey is too slow or stops, he actually goes under his tail and bites uh you know, his butt.. and hangs on while the turkey drags him around trying to get him off.
Have to say I did hit my tolerance point last week when the male guinea decided that one of my free range peacocks was in need of brutality(again, no apparent reason.. they were seemingly fine with each other and wham!) and he was quite vicious about it- the peacock would try to escape by flying up onto a pen or a tree but the guinea would be right there and he really would not let up, the peacock was getting exhausted and the guinea was using that as a chance to really bite and do his "slamming" thing repeatedly so that was it- grabbed the guinea and clipped both of his wings. It's his last warning..
So there you have it.. may be ok like many will come and tell you but honestly it also could turn out not to work perfectly well. Just won't know until they're all grown up and see.