It is not always easy to figure out which title to use. Even family members and media, as well as people who are more or less experts, like me, sometimes have difficulties. Just say: it is complicated. And if you’re not sure, better check or ask someone with more knowledge.
I am always surprised when seeing mistakes in the titles in death announcements, especially in the United Kingdom. The biggest mistake is “Lady (first name) (family name)”, often used for women married to a Sir or wives of a Lord. Actually it should be “Lady (family name)”, unless the person in question is the daughter of an earl, a marquess or a duke.
Dutch articles, like this one, tend to call the Crown Prince of Saudi Arabia, Prince Mohammed bin Salman Al Saud, simply “bin Salman” in their headlines, as if that’s a kind of family name. Bin Salman actually means “son of Salman” and is surely not intended to be some kind of surname or title. Recently, I noticed a journalist using “Lalla” as a first name for Princess Lalla Salma of Morocco. Lalla is actually part of the title, and Salma is the first name.
Using the wrong title is not done either. Often one can read “Prince(ss)”, even if someone is a “Crown Prince(ss)”. Recently a Dutch magazine online wrote about King Haakon, instead of Crown Prince Haakon, which is of course pretty funny.
Once I even caught a Belgian royal magazine, not existing any more, inventing a title, that actually doesn’t even exist. “Aartsgraaf” (Arch count) where they should have used “Aartshertog” (Archduke).
I am sure there are many more examples.