Although Sir John and Mrs. Jennings’ teasing distressed and mortified Elinor, I don't think that was really their intention. If I remember correctly Mrs. Jennings says at one point that young people like to be teased, so perhaps their intentions were good, maybe they thought Elinor would be pleased being teased about the letter "F" as Miss Steele later was when they teased her about the Doctor. Sir John, Mrs. Jennings and Charlotte may not have been the most intelligent people, and Mr. Palmer not the most polite but they were very kind to the Dashwoods. I was struck how generously they behaved when Marianne became sick, they feared for the baby so the Palmers left their own home, instead of sending Marianne away as John Dashwood and Fanny would have probably done. In spite of their being rather foolish I think Mrs. Jennings, The Palmers and Sir John are really good people John Dashwood on the other hand is a selfish and heartless fool.