Japanese girls, even ones living up mountains and going to boarding school will be used to things like spagetti, curry and hamburgers, but they might find the meat to veg to carb ratio quite different from what they are used to, so having a rice based meal and allowing seconds on rice might be nice for a meal fresh off the plane when tummies are not super excited about new food. perhaps you can borrow some short-grained Japanese rice from your neighbors wife (unless of course you already have some), and either cook it in a rice cooker if you have one or ask her how she usually cooks it. I am trying to think of something simple you or the girls could make with ingredients you might already have on hand - a bowl of rice with a sunny side up egg, fried in butter w/ the yolk still runny and served with soy sauce. I'll bet you have that on hand!
at 14, they likely have a good deal of English grammer under their belts but little speaking experience - they will have been training for English tests rather than converstaion, so speak clearly and give them time to think of their responses. they really do know a lot of English (but likely American English), I expect, even if they are shy at first.
I can't think what else to tell you - they will be used to cold weather as we are still deep into winter right now and there isn't generally much by way of indoor heating 'round here. They will probably want a shower or bath before bed rather than in the morning. there are a few minor manner issues that might seem a litte rude to you - the one that always gets me is not waiting 'til everyone is at the table before eating.
all in all I wouldn't worry much about it, especially if there are two girls to keep each other company. have fun!
Sara, mama to a 3 yo dd since 2008 :