(Answered by Gene Popa)
George asked both of them. Paul said he would participate, but only if the other three Beatles agreed to legally dissolve their partnership (which is what McCartney was at that point suing in court to achieve). George declined.
John actually showed up at the rehearsal, but when he asked what Yoko’s role in the concert would be (obviously expecting she would get a solo set of her own), George replied, “I would like her to enjoy the show.” In a huff, John and Yoko stalked out and did not perform.
John and Yoko did attend the film’s premiere in New York City, and he seemed to be enjoying himself by clapping and cheering the performances on the screen. However, during Bob Dylan’s performance segment, John and Yoko suddenly stood up and left the theater without explanation.
Every Moment Has A Song 