Add vegan butter and shortening to a mixing bowl. Using either a hand-held mixer or a stand mixer with the paddle attachment, beat on medium speed until light and fluffy. Add the vegan cream cheese and beat for another minute or so, until combined.
Add the powdered sugar 1 cup at a time, beating in between addition. Then add the lemon juice and milk. Beat for another minute or so, until all ingredients are combined and the frosting is light and fluffy.
Cover and refrigerate for 30 minutes or so, to allow the frosting to thicken.