When I use the roman numerals on a webpage for ancestry they appear as letters as well.
This is my first time working with Font Creator and it is frustrating. It appears I do not have the simple tutorial edition to learn the program.
I understand FontCreator can feel overwhelming at first, especially if this is your first time working with fonts.
This tutorial should help you get started:
Creating a Font and Editing Glyphs
FontCreator also comes with a comprehensive user manual, so it is worth reading the sections that are relevant to what you want to do, especially Insert Glyphs and Insert Characters.
Regarding roman numerals: fonts work through Unicode codepoints. Text processing software and web browsers do not use the glyph name to decide what character to show; they use the character’s Unicode value. So if you draw a roman numeral in the glyph slot for the letter I, it will still behave as the letter I. If you need actual roman numeral characters, you should add or edit the proper Unicode characters for them.
OpenType features can also substitute one glyph for another, so the visible glyph is not always the same as the typed character. Some general knowledge about how fonts work will definitely make FontCreator easier to use.