I have geese, ducks and hens and they all live in harmony. At one stage I used to let the geese sleep with the ducks at night but during the breeding season they became quite vicious and so for safety we now lock them up separately. I can see you having no problems with introducing the geese. I have 17 ducks, 10 hens, 1 cockerel and 5 geese and they are all totally free range too.