Rosanna Spearman is often interpreted as Rachel's less fortunate double. She's a reformed thief, a servant, and has a disability – whereas Rachel is the soul of honesty, rich, and beautiful. But they're both in love with Franklin Blake, and both refuse to speak out even though they know that he took the Moonstone. Poor Rosanna ends up throwing herself into the quicksand, while Rachel ends up getting married to Franklin.
If Rosanna is Rachel's unfortunate double, Ezra Jennings is Franklin's. Both are associated with foreignness: Franklin because he was educated outside of England, and Jennings because his mother was a foreigner. Both have been falsely accused of a crime. But Jennings was unable to clear his name, and lost his lover as a result. Franklin, on the other hand, is able to prove his innocence and get married to the girl he loves.