There are rules for the pronunciation of these names. Until a century or two ago, the Latin language was widely used Europe for all sorts of learned discourse. It was spelled the same everywhere, but pronunciation varied quite a bit from country to country. In England, there developed a traditional English pronunciation of Latin, quite different from the speech of Caesar, which had long been forgotten. Modern scholars have deduced the ancient, classical pronunciation, and this is what is usually given when Latin is taught in schools.
Few experts use either system exclusively.
In Latin, vowels may be either long or short. Latin also has several diphthongs, written with two letters but pronounced as a single sound. The diphthongs ai, eu, oi, and ou are used in words borrowed from Greek. In Latin words not of Greek origin, the two vowels are pronounced separately. For example, one hardly ever hears the e in tectorum being pronounced as a long vowel, although it is long in Latin.