How old are your Guineas? Guineas like routine, but you have to help them establish one, or as you already know they will establish their own. You could temporarily wire off the area under the coop that they are going under to sleep at night, until they get with the routine of going in each night. Consistently giving them a treat like millet or a wild bird seed mix containing a lot of millet once they are in the coop each evening, (using the sun going down as a visual cue for the birds to understand it's time to go in) helps condition/train them to going in, and getting a treat each evening (at approximately the same time) gives them something to look forward to. I only feed that particular treat once they are back inside tho, no where else. I usually close my coops/pens once everybody is out to free range so that the birds cannot come and go as they please (they all have a water source outside as well as in the coop)... I find that closing the coops/pens up each day really encourages them to want to go back in each evening when I open the doors/gates back up (it creates coop and feeder separation anxiety... and they are looking forward to their treat). Also you could try using a bale of straw in front of the door, instead of the ramp so they can just hop up... navigating the ramp at dusk may be what's intimidating them, so you'll want to start getting them in before it's so dark that they choose to bed down under the coop or lay on the ground in the pen. The light on in the coop (at least until everybody is in at night) is also a good idea... Guineas are blind in the dark, and won't move around much at all if they can't see. (I always get my birds in before dark, but I do use a strand of red LED rope lights in my coops that are on a timer... it gives them just enough light to see if they get bumped off the perch or spooked for some reason. They can't break the lights, and there's no fire hazard... plus they are inexpensive to run).