I love coffee, and am very particular about it at home. However, when I travel and am a guest in others' homes, I don't expect my hosts to provide it, especially if they don't drink it themselves. I think providing instant is a lovely gesture, but I'd probably personally prefer to visit Starbucks or the equivalent as instant is not strong enough for my taste. I'd touch base with your guests ahead of time and let them know that while you don't own a coffeemaker, there is a Starbucks nearby in case they'd like coffee, and they can plan accordingly.
I'm taking a trip next week and I'm planning to pack my own freshly ground beans along with a travel French press, so it's possible that your guests might also be planning to provide for themselves on the coffee front. It's also possible that I'm too attached to my coffee, lol!