Forgive me for being such an amateur, but I’ve made regular, bold, italic, and bold italic versions of a font, in four separate glyphs files. Exporting them and installing them in Font Book merges them all into four faces of the same font family, but is there any way I could have them all in the same Glyphs file (or at least .otf file)?
You can merge the upright in one and the italic in one file each, so you have two .glyphs files. Please have a look at the manual on how to set up a Multiple Master font.
And .otf files can’t contain more than one style.
So I probably shouldn’t try to put all 4 styles into one glyphs file then?
No, put them in to files. One for the upright and one for the italic, Everything else is not working well.