Short answers, pulled from the story.
Brian Epstein died of a drug overdose on the 27th of August 1967. His death left the Beatles disoriented and fearful about their future because they relied on him to mediate conflicts while letting them pursue musical ideas.
The sessions for The Beatles began at Harrison's home in Esher in May 1968. These sessions marked the first appearance of Yoko Ono in the studio and reflected the development of autonomous composers, musicians, and artists within the group.
Harrison informed his bandmates that he was leaving on the 10th of January 1969 after eight days of rehearsals at Twickenham Film Studios. He felt stifled by combined patronising from McCartney and estrangement from Lennon.
McCartney distributed a press release to select UK journalists on the 9th of April containing advance copies of his solo album McCartney. Newspapers worldwide interpreted remarks as announcement that band had broken up when he talked of break with Beatles and having no plans to work with band in future.
Lennon made his decision to leave the Beatles on the flight back to London from Toronto Rock and Roll Revival on the 13th of September 1969. He privately informed his bandmates at a meeting at Apple on the 20th of September that he was leaving.
McCartney filed lawsuit against other three Beatles in London's High Court of Justice for dissolution of partnership on the 31st of December 1970. The case opened Chancery Division the 19th of January 1971.