I think you are being very thoughtful.
I am also an American coffee drinker, but I don't drink coffee every day of the week when I'm at home (I don't bother with it on weekends, usually). I am also quite happy to substitute strong black tea (with milk and sugar) for coffee, if that's what's available. I'd much rather good tea than bad (or instant) coffee. I drink coffee mostly for the taste and the comfort of it (it is nice to start the day with a hot drink), rather than the caffeine.
Since you don't live in the US (I'm assuming), I will also point out that many American travelers know that food/beverages aren't going to be exactly what they are used to when they travel elsewhere. Especially if they have done any traveling outside the US before. Even those who aren't aware of it would, I think, be more than fine with knowing there's a Starbuck's nearby.
I think that if you (or your friend) have the ability to contact the houseguests before they arrive, just mention that you are not a coffee drinker, but you do have tea, you could acquire instant coffee, and there is a Starbucks right around the corner. That will alert them to the fact that you don't have drip coffee in your home, but that there are some options if they feel they need it first thing. And if they are the type of people who really won't drink instant coffee, they have the opportunity to say something before you've actually purchased it.