the fonts with the small nx icon on the left of the name are single stroke nx fonts, the ones with the A on the left of the name are standard windows fonts.
I think you should prefer the nx ones because they are single stroke and the resulting single-trace tool path is simpler.
It is possible to add character to nx fonts, the nx font files are in ...\NX N.NN\UGII\ugfonts, where you can also find an utility (ugfontc.exe) to convert compiled fnx font files into source fnt font files (ugfontc –u compiledFontFileName.fnx)
Once you have the source fnt file you can open it with a standard editor, add the characters you need and then convert back the source fnt file into the compiled fnx file (ugfontc –c sourceFontFileName.fnt).
However, adding characters is not simple and you could also have missing characters problems if you exchange files containing “custom font” text with other sites.
Since iso-1 has the characters you need, is single-stroke nx font and is also looking good, I think the best choice is to go on with that one.