I found one of the most confusing aspects of reading anything written in the mid 1800s is the way titles, ranks, and names were used. Siblings even addressed each other by title. In letters a person might be mentioned with a rank and last name, or a title and first name, or just one of either. To try and get an understanding I would recommend this website: Peerage Basics &c.
Laura A. Wallace has done a great job setting it all out. It takes over a dozen pages, but at least it’s all there. I still don’t have it entirely straight, and I think there have been some changes over the years, but now I can usually determine who is being referred to in each passage.

As I write out the diary entries and letters into narratives I try to simplify the use of all the various honorifics to make it easier for people to read. Below you will find a list of terms as used in England in order of seniority.

Sir Arthur Wellesley, 1st Duke of Wellington, by T. Lawrence. The son of an earl, he was technically demoted when knighted in 1804, then made a baron, then viscount, then an earl, then marquess, and finally a duke in 1813. Kate Tattersall also went through a bit of a demotion and promotion process, but despite winning laurels of honour for her service, her highest rank was simply for being the daughter of an earl.

Royal and noble ranks, titles of Peerage
King and Queen
Prince and Princess
Duke and Duchess
Marquess and Marchioness
Earl and Countess
Viscount and Viscountess
Baron and Baroness

Titles of the Landed Gentry (Commoners)
Baronet and Baronetess
Knight and Lady
Esquire and Lady
Gentleman and Lady