Is it rude to give Japanese families money?
Japanese people are polite so it would be best if you learn a little bit more about their culture which will be backed up by some informations you obtain from the Japanese embassy. When you get to the Japanese couple’s residence, leave your shoes, sandals or slippers outside the door and wipe your feet before entering the house. When saying thank you, the degree of your vow shows the degree of your respect and when you speak don’t make too much hand gesture because they find it rude. I know that your question is only regarding the giving of money but knowing a little bit of their culture goes a long way. Enjoy your trip.