That's pretty typical with guinea fowl, they never really get as domesticated as chickens do, and always retain that degree of wildness. I found that raising guinea fowl with chickens keeps them a little more domesticated. The guineas may follow the chickens into the coop at night, but not always. Also, guinea hens often go off into a more weedy area to lay their eggs. Chickens are bred not to go "broody" and not sit on their eggs, but in a flock of guineas one hen may sit on all of the other hens' eggs. That hen may disappear for weeks and then appear followed by a couple of dozen of chicks. Unfortunately, guinea hens are terrible mothers and don't pay much attention to their chicks as they slowly disappear.
The only way I found to get guinea fowl into the coop at night is to put their favorite feed in the coop at night. the guineas MIGHT go in there at night to get some treats and MIGHT end up sleeping there. It only works sometimes. Guineas just like roosting in trees.