Why does Tituba come up with the names "Goody Good" and "Goody Osburn" as the two women she saw consorting with the devil?

Tituba probably comes up with the names of Goody Good and Goody Osburn because those are the two names suggested to her as potential witches as she is being interrogated and threatened. First, she merely tries to deflect attention away from herself, saying to Mr. Hale,

Mister Reverend, I do believe somebody else be witchin' these children.

Tituba does not name names here, as she seems just to want the discomfort of negative attention to be moved off of herself. However, Hale continues to press her, asking about others, as though Tituba's story would be doubted were she unable to provide the names of other people she saw with the Devil. Her owner, Reverend Parris, begins to press her for names as well, and, finally, Thomas Putnam asks,

Sarah Good? Did you ever see Sarah Good with him? Or Osburn?

It is clear, therefore, that Tituba will be believed if she names either of these two women, because they are already suspected of working with the Devil to kill the Putnams' babies. Next, Hale takes her hand and speaks so kindly to Tituba that it shocks her: she is not used to such kindness. He tells her that she will have a special place in the village if she helps them to "cleanse" it and that "God will protect [her]." It is clear that they are not going to let this go until she gives them the information they want, and so she does, naming Good and Osburn.

Sarah Good and Sarah Osburn are two women with bad reputations in Salem. When questioned by Reverend Parris and Mr. Putnam about speaking with the Devil, Tituba realizes that the best way to deflect suspicion from her own activities is by accusing others of witchcraft. As Goody Good and Goody Osburn have such bad reputations, they're ideally placed to take on the role of scapegoats. If Tituba were to accuse anyone else of such diabolical practices, the charge might not stick. But accusations of witchcraft against these two women have an air of plausibility about them, especially Goody Osburn. She acted as midwife to Mrs. Putnam, and the Putnams are convinced that, through the practice of witchcraft, Goody Osburn was responsible for the deaths of their infant children.