In The Westing Game by Ellen Raskin, who was Mr. Westing pretending to be?

During the course of the story, Mr. Westing pretends to be four other people, and those four people are known as Barney Northrup, Julian Eastman, Sandy McSouthers, and Sam Westing.The last alias, Sam Westing, shares the same name as Mr. Westing but is an alias nonetheless.
As Barney Northrup, Mr. Westing disguises himself as the salesman responsible for selling the apartments at Sunset Towers. He is described as "a good salesman," bucktoothed with a slick black mustache.
Julian Eastman, meanwhile, is supposedly the President and CEO of Westing Paper Products Corporation. He wears business suits and rimless half-glasses, has a small limp, blue eyes described as "watery" and "hard," and slightly uneven, white teeth.
Sandy McSouthers is the doorman at Sunset Towers who was fired from the Westing paper mill. He is broad-shouldered, obsequious, and likes to gossip.
And, finally, Sam Westing is the man who died and left the details of the Westing game in his will. He is remembered as "the mysterious industrialist who disappeared thirteen years ago" and who was found dead in his mansion. He was the son of immigrant parents and was orphaned at the age of twelve. He is renowned as a man who built a hugely successful business from next to nothing.