There's no definitive answer to this... Some people have no problems at all housing Guineas and chickens together, some have nothing but problems. There's quite a few past threads here on the Guinea Fowl forum that have testimonies and opinions that go both ways on this subject. If you have time, reading thru them may help give you an idea of what you could be facing.
Having the biggest coop and an attached covered run possible, with plenty of places for picked on birds to hide behind (but not get trapped behind), lots of roosting space, 2 feeders and 2 waterers, plus plenty of free range time for everybody definitely helps. Over crowding is never good when Guineas are concerned, even if you keep only Guineas. They need at least 4 sq ft of floor space in the coop, 2-3 times that in the run as adults. The Guineas will need to be raised on high protein game bird, turkey or pheasant starter feed for the first 6 wks and then a game bird grower feed until they are 12 wks old to be able to grow, feather out and develop at the proper rate without developing any health or development issues. Chickens can be raised on the same feeds and will supposedly pass the extra protein without any issues, but there are some that argue this point. (I do not own chickens so I cannot speak from personal experience as to whether it's true or not... but I do know plenty of people that have had no issues with their chicks eating the high protein starter feeds). If you can start with chicks and keets of the same age/size and raise them together, they may be fine and bond as a flock and never have any issues. Most likely the first breeding season will give you an idea if you are going to have any aggression issues or not. It's usually the Guinea cocks that start causing the problems, but the rest of the flock can tend to have the monkey-see-monkey-do mentality and follow suit if there's one aggressor in the group. But then again, your rooster or roosters could be the aggressors just as easily. It really varies from flock to flock, coop to coop. Not everyone's coop/run situations and birds' temperaments are exactly the same. Having a back up plan/place to move the Guineas to is always a good idea if problems within the flock do start happening.
