The murders were carried out by what I guess we’d now call “home invasion.;”...................................
A fifth person, Charles “Tex” Watson, was tried separately after he fled the jurisdiction and fought extradition; a sixth, Linda Kasabian, turned state’s evidence and testified against the rest.
Although they didn't know it at the time (or at least Linda Kasabian testified they didn't know it at the time), the Manson Family participated in a bunch of what they called "creepy-crawly" missions that were really 'dress rehearsals' before the first murders. These 'missions' included sneaking into houses and stealing things while the inhabitants were asleep. That prepared them to go into the houses for the eventual murders without being detected until it was too late.
Charles Watson was the person Charles Manson put in command of the expedition to do both of the sets of murders. He got the general 'outline' of what to do from Charlie, but the details were up to him. After the murders, he ended up back in his home town. Since he was known there as a former A student, had cleaned up his act from his days with Manson and his family was 'not the sort of family you expect a murderer to come from.' That (plus going into a catatonic state, going down to a dangerous weight) allowed him to escape being sent back to California until after the girls had been tried and he knew what evidence had been used against them and who had claimed what. So, by the time he was tried, he knew pretty much what they had evidence of him doing.
From what I remember, Linda Kasabian had been chosen to go on the Tate 'mission' because she could drive and had a driver's license. Charlie didn't want the police to stop the car on the way there and not have a licensed driver in it. by the time of the murders, she was aware that to not do what Charlie said to do could very well mean you would never be seen again.
She also drove the car to the La Bianca house, but instead of being ordered in there, she was supposed drive the car to find the apartment of an actor show she knew; she and Susan Adkins were supposed to murder him. Linda testified that she knew which apartment was the actor's, but knocked at another door instead and that 'mission' was abandoned. I don't remember for sure, but I think Charlie was with them.
Charles Watson had been ordered by Charlie to make sure that everyone participated in the Tate murder. Linda's only participation was driving the car, so she didn't actually kill anyone. The evidence and the testimony of the other 'Manson girls' bore that out. Susan Atkins was taken into custody for arson when the Manson 'ranch' was raided. While in custody, she bragged to one of the other prisoners that she had been a participant at the Tate house. She also said there was one girl there who had not participated, which she was upset about. That girl was Linda Kasabian.
Linda testified she had tried to stop the murders by saying she heard noises and they needed to leave. If I remember right, the others did agree that she said that, but they had continued with the murders anyway.
So, at any rate, she was the only person who had first hand knowledge of what had happened without having actually killed anyone, and had remourse for her part in the whole thing, which made her a good witness for the prosecution.