How we cite our quotes: (Chapter.Paragraph)
Quote #4
"She would take them bathing from the boat, she would have a picnic supper at her cottage in the cove. They made love to her of course; who would not? She laughed, she would come back and tell me what they had said, and what they'd done. She did not mind, it was like a game to her. Like a game." (18.135)
Mrs. Danvers is confirming Maxim's claims that Rebecca was sexually promiscuous. We don't see any reason she would lie, unless Rebecca was lying to Mrs. Danvers. Notice that Mrs. Danvers' claim comes conveniently before Maxim's, so Mrs. de Winter is already primed to believe it when he tells her.
Quote #5
"[Rebecca] sat there, laughing, her black hair blowing in the wind; she told me about herself, told me things I shall never repeat to a living soul." (20.35)
Well, we wish he would tell a soul, because these inquiring minds want to know! Since Mrs. Danvers has already told Mrs. de Winter that Rebecca had affairs, it's easy for Mrs. de Winter (or readers, anyway) to assume a sexual context.
Quote #6
"If I had a child, Max," she said, "neither you, nor anyone in the world, would ever prove that it was not yours. It would grow up here in Manderley, bearing your name. There would be nothing you could do. And when you died Manderley would be his. You could not prevent it. The property' s entailed. You would like an heir, wouldn't you, for your beloved Manderley?" (20.77)
Max is quoting Rebecca, and telling Mrs. de Winter his motive for murder. If we believe him, Rebecca is claiming she plans to pass off another man's child as Max's. There isn't any Maury Povich running around with his who's-the-daddy DNA kit, so if she was pregnant, she would have been able to do this easily. "Entailed" means that Manderley can't be sold, and Maxim has no control over who gets it. It will automatically go to his first-born son.