Do the Amis have to wear masks in public transport-buses etc?

i think you mean the amish.  they do not participate in public transportation, and some cannot even SPELL it. 

The Germans call the Americans " amis"

Amish use buggies, bikes and allocated transport but if they fly or have to use public transport then they are bound by 'English' rules. 

No one has ever heard of these mythical creatures known as Amis, or are you talking about Religious people known as Amish?  I doubt they use Public Transport, but if they did, they too would have to wear a face mask, unless they are exempt for medical reasons.

Who or what are the Amis. I have never heard of them.

I have no idea.