We're discussing these two characters together since they are sort of a package deal. In fact, it's sometimes hard to tell them apart. They live together (with their dogs), and they both enjoy telling fortunes. More importantly, they're both former actresses who love to talk about their days in the theater.
"I played Portia once," said Miss Spink. "Miss Forcible talks about her Ophelia, but it was my Portia they came to see. When we trod the boards." (2.8)
This theatrical flair can be amusing, but it also leads to, well, self-involvement. Miss Spink and Miss Forcible both call Coraline "Caroline" and they don't really seem to listen to anything she says:
"She's vanished under mysterious circumstances," said Coraline, "and I believe my father has as well."
"I'm afraid we'll be out all day tomorrow, Caroline, luvvy," said Miss Forcible. (5.15-16)
Even still, the two actresses actually end up helping Coraline quite a bit. Without their fortune-telling, Coraline wouldn't have known that danger was lurking. And what's more, they give her that handy stone with a hole in it for protection. This stone turns out to be a powerful tool which helps Coraline escape from the other world. In the end, despite their flakiness, Coraline feels a strong bond with these two nutty ladies. We think they'll stay good friends in the future. Especially now that they finally know Coraline's name.