It is a goose causing the trouble. She is small and her features are totally different to the gander. She is more like the 5 definite geese I have but smaller.
Vent sexing geese is fairly easy and in your case i'd say its definitely worth doing.
going by looks alone with embdens is a bit hit and miss even for experienced goose people, I certainly wouldn't be confident sexing them visually.
it can often be a case of just watching their behaviour rather than going by their appearance.
How definite are you about the 5 geese?
From your description, your small troublemaker 'goose' sounds to me like a young gander
They will need sorted soon, they'll be laying in about 3 weeks and mating should be starting very soon if its hasn't already.
Good luck! sounds like you have a bit of a handful with that lot!