Complex sentence: The Beatles are said to have been pleased with the result and attended its highly publicised London premiere, every one of The Beatles thought their own voices (narrated by actors) were not quite right, whilst saying that the other three were perfect.
Split into simpler sentences: The Beatles are said to have been pleased with the result and attended its highly publicised London premiere. Regarding the voices provided by voice actors for The Beatles in the film, each one of The Beatles thought his own voice was not quite right, whilst saying that the other three were perfect.