Josh isn't happy about having to live with his dad in Chicago, but his parents seem happier when he agrees to their plans. Josh's mom goes to Florida to care for his grandmother who has fallen and needs her care. It may sound crazy, but Josh would rather be playing cards in a retirement community than kicking around Chicago with his dad.
Then he gets off the plane. And sees the parrots. And the bad dye job. And the gold sunglasses. And he sees older women taking a second look at his dad. Aka "The King".
Josh is fairly self absorbed, not unlike many 13 year olds. He feels like he needs to be independent as well as protective of his dad from his over-worrying mother, so Josh doesn't tell his mom the most salient points of change about his dad: he lost his job and he's impersonating Elvis.
All Shook Up is entertaining to a point, but Josh isn't very engaging or lovable (he's "poor me" pathetic). His strategy for getting in with the jocks by the vending machines at the school cafeteria isn't accompanied by any descriptions of who those students are, and he makes no internal observations of who his new "friends" would be after sitting for by himself for weeks watching them. When Josh is selected for the baseball team, there's no recognition that being picked by David brought Josh closer to achieving his "goal".
I remember the days when practically anything my parents did out of the ordinary was embarrassing at some level, but then we'd compare notes among friends - not further isolate ourselves all the while wishing for inclusion while rejecting the friendship overtures offered. Perhaps Josh's reaction was in line with his self-esteem, but he seemed to take great exception to his dad. Josh does make steps toward redemption and Gladys provides lighter fare with soul. Ivory is both wise and innocent and possibly a little shy, but it still seems like she would have greeted him face to face earlier and had some awareness of Josh's sensitivity to his dad's new vocation.