Expecially because I'm learning latin.

If you're talking about their canon names, I'd look at the names used in foreign versions of the book. Maybe try Italian? There's always the standard method of sticking an -us on the end of everything, but it tends to look a little clumsy. Some names, such as Hermione and Lupin, are of Greco-Roman origin, so there should already be methods of handling those structures. Another option would be to translate the names into others with similar meanings, but that might make it hard to tell who's who - an issue that My Immortal does not need exacerbated. There's probably research as to how Romans handled the issue of non-Latin based names; I'd suggest trying to find some of that. You also might want to take a look at ecclesiastic Latin, assuming you're working with a more classical source.

This, however, is My Immortal, which among other things, renames pretty much everything. For characters whose names have actual meanings, I'd translate it directly - i.e., B'loody Mary becomes Maria S'anguinea, Willow becomes Salix. Ebony should probably just go to Ebonia, however, in order to maintain the many, many variations used.

That said, if this is your first project, you might want to start with something shorter and better spelled. Figure out how you want to translate names, before you have to worry about things like malapropisms that are meaningless in other languages.