We keep lots of Muscovy ducks (lots) and have Steinbacher Geese (like Greylag but paler). You don't say what sex or breed your geese are. I'm guessing its a trio, so with a male. The males only get aggressive when their ladies are in season - Jan/Feb through to end of May - our gander wants to rip your head off. After that he goes back to being his easy going self (with us humans).
They are always meanies with the ducks - Muscovies are quite big and are more goose like than duck like so they can take it, but I have heard on several occasions that during the breeding season geese can literally rip apart a small call duck. Geese like to rule our pond and will bully our ducks and ducklings just for the sake of it, but they keep pretty quiet and in the background most of the year so that makes them tolerable.
I would either keep a breeding pair - geese can live to a very old age and will partner for life, or just keep the females, they won't be aggressive, particularly without the male.
Geese are easy to keep and economical, you don't have to give them much as they love grass. I would try it out and see - if they get too aggressive in spring, eat them, they will of course but you could try putting up with it - keep well out of their way and see how they get along with your other ducks. Remember geese are very tasty but there's not a huge amount of meat on a goose - I would try and breed from them and eat them when you have quite a few.
Remember not to mix your geese breeds as it can lead to serious fighting.