@Kedar: I guess you are just a 1 girl type of guy. If it were me, I would say yes, and at least try to learn something of the experience. I'm not sure about Japanese culture, but in America, going to a dance does not mean anything, lol. You can go as friends, but make it clear at first. That way, you can see if they are nice or not. But really, their father and brothers make it not worth it.
I remember with the Korean girl I dated, I drove her home after a movie at midnight, and her brother came outside..."Do you know what time it is? Get inside the house!!!" I was like...Hm...."Hey man, sorry, I didn't know she had a curfew..", the brother replies..."it's not your fault, SHE should know better"...after that...i was like...OK, i'm not going to deal with this guy, lol, I'm outta here.