No matter how cruel Kevin was, what Randall did to their mom was awful and dredged up old feelings (no therapy in Pearson family when young) Kevin ran to Randall any time he called, twice or three times we know about with panic attacks. That office scene was heart breaking and the last time, he was there. He loves his family, his girls. What Randall said was dad never was proud of you, died thinking you were a loser, you are not a good actor, not a good person, and I am. So Kevin used the truest emotion he had in his angst. Since birth, Randall was hovered over by his mom, partly because he was different in looks, she knew he'd need more attention, he was anxious, she knew she lied about his parents, she was always trying to fill holes. Kate, enough said, was super spoiled by her Dad, nothing her mom could do would erase that. Kevin, the pool incident broke my heart, he was forgotten. He saw his siblings in a child's mind, Randall is smart and gets accolades, Kate just exists and is doted on by Dad, I have to do things in a big way to get noticed.
They obviously make up, but Randall didn't have to take care of Rebecca. He hovered the same way. After the initial grief she should have gone to therapy, gotten a part time job, joined groups, tried to find friends. He wasn't the golden boy, he wanted to be a savior.