This sounds like a really exciting opportunity. It'll be great to have the opportunity of working with Tibetan monks.
I suggest you find out all you can about the monks and their reasons for learning English before you travel. You can ask about their level and their previous experiences learning and using English.
You should also ask about how they will use English in the future. Many monks now travel in order to visit Buddhist (I guess they're Buddhist) centres around the world, to attend conferences and to teach others about their religion.
Once you know their level and reasons for learning English, you will be able to choose materials for teaching them. At that point, you can write in again if you like.
I don't know of any materials designed specifically for this market. I suppose they'll want to learn about: introducing themselves; useful language for airports and travelling; describing their religion. You can plan your lessons around these themes and others, incorporating language and skills work.
All the best,