How do I know they are ready to free range?

I'm curious why your guineas 'hate' their coop. How big is it? How much lighting is there inside? Have you ever caught them inside of it or has anything else traumatic happened when they went in?

Before you let them out, make sure you can 'herd' them inside their run without too much drama/scattering. Do you call them to you for treats and do they run to you? Is there a large door to the run which would be easy to drive them back in through after?

Once you do start letting them out, start with short trips out, and then get longer each day. Make sure to bring them in an hour before sundown so they don't take to roosting in trees.

Aside from that, others can help you with their experiences and advice :)

http://www.guineafowlinternational.org/articles/

 Has articles about training guins to herd, come when called, and a bunch of other interesting stuff.  They also have a very good forum, just ignore the fights about color.

IMO... You are going to need to stand your ground, and not cave in... and basically restart their training and establishing a routine for them about cooping up each night. They've already learned that they can choose to do as they please, and I'd say it's highly likely they will established their own routine of choosing to roost in the trees or on roof tops (where owls will most likely get them) and once they start roosting where they want they will most likely refuse to return to the coop/run all together. So it's better to nip it in the bud now, than finding feather pile after feather pile and having to replenish your flock in a few months if you start free ranging them at this stage.

If the coop is of adequate size, and they have plenty of roosting space and you want them to roost safely in the coop each night... then I'd feed, water and give them treats only in the coop, and yes force (herd) them all to go in every night at approx the same time, and lock them in every night, with an extra yummie treat as a reward consistently, for several weeks. They can go out in the pen each day, but into the coop they need to go before dark. Sounds like you may have a rebellious flock... and food persuasion goes a long way with teaching them to cooperate. They may need to skip a meal or 2 to once again appreciate food and become a little more cooperative. May sound a little cruel, but not as cruel as being painfully pecked at, clawed at, chewed on, shredded or ripped apart by a predator.

If you decide it's too much hassle to start over, they may do fine with always roosting in the run depending on your predator load in your area, but I'd be extra diligent about getting them back into the run each night. One thing to keep in mind tho, is that predator season is coming up, they will have young to feed, and predators can and will reach thru the run's wire to get your birds, and if there's any possibility of a predator digging under, believe me, they will. It's in your birds' best interest that they learn it's a good thing to get locked up safe each night... unless you are ok with the probability of losing your birds one by one.

Yep tough love indeed, lol.

I'd raise their roosts, Guineas always prefer to roost up as high as they can get, just make sure you have soft bedding for them to land on and that they have enough room to safely jump down from as high as you raise the roosts (and that they won't bump their heads jumping up to the roosts). I run a string of red LED rope lights in my main coop, it gives them enough light to see well enough to get up on the roosts, or back on the roosts if they get bumped off or spooked, but supposedly does not disrupt their sleep pattern.

getting them in right before dark, consistently at approximately the same time every night helps ingrain it into their brains that it's time to go to bed. I have a general feeding time for all animals on my ranch, I've integrated that time with coop-up time for all my flocks. They've adapted very well, and if I am late, they are usually on top of the coops, up in the driveway area or waiting at the gates squawking at me to get my butt out there and let them in and feed them (once they start free ranging I close the coop/run so they cannot come and go as they please (or eat all day long)... kind of helps develop a little separation anxiety from the coop and feeder, lol.

There is usually one low bird in the flock that kind of gets rejected by the others, but now that breeding season is right around the corner it's safe to assume that one of the males will claim her as his and the 2 may pair off keeping their distance from the rest. If they are not letting her eat/drink much, having two feeders and waterers helps.

Good luck with the tough love!

Guinea's can be a trip. I have 9.Oh the heck I paid trying to get them back up. I won't even tell you but I was pulling my hair out. I asked for help on here and Peeps told me what to do and it still works. They are the most hard headed stubborn birds I have ever had. But I definetly love them. And can't wait to have more.

We have a couple dozen guineas ranging in age from six months to a couple years, and have learned that they really prefer going into light.  If you have to coop them after dark, trying putting a bright lantern in their coop before you start herding them in.  That will ease their mind that there's no boogie-predator in there.    We've also learned that ours love holly berries--the bright red is easier to spot then seed and cheap if you have any hollies!  The advice everybody's already given is excellent as to making them go in at night, and giving them a roost as high as possible.  My only other addition is that if I understand correctly, these guineas were not raised on your property?  Is so, the usual rule is that 'mature' guineas of 4-6 months or older must be kept confined to their coop/run for six months before you allow them to free range.  For chicks it is six weeks, but adults take much longer.  That way you make sure they've imprinted where home is and will come back.  Any sooner and you will most likely lose them.  Best of luck!  Guineas can be flighty and a bit schizo when they're young, but settle down a lot after the first year.