Do you think Happy and Biffʼs ideas (ie. getting funding from Oliver) are realistic? Where do you think they get

No this is not a realistic idea. Like his father, Biff lives in a fantasy world. It is true that Biff once did work for Oliver but Oliver hardly remembers Biff. Biff was under the delusion that he was somehow partners with Oliver in business. Biff would get these grandiose ideas from his father.