How to I add macrons to a font kit - for Maori language (New Zealand)

We are using the font Aktiv Grotesk for our website but need to add macrons over certain letters for words in the Maori language.  The letters appear in a different font whenever a macron is selected.  Research online suggested uploading Adobe Typekit (with all characters selected) but it doesn't seem possible to add a custom font to Squarespace 7.1.  Any suggestions would be greatly appreciated.  Thanks

I would really like to know how to do this too!