Hi Marcus and welcome to our forum.
As you have been in this relationship for 12 months and you've only just found out her age it would appear that there has been quite a bit of deceit on the part of your girlfriend and her family. To continue with the relationship with a view to to making it permanent would doubtless involve more lies and deceit only this time involving you. Do you really want that.
Lets face it to come clean now would result in jeapordising the sisters marriage to the Japanese husband. I cant see the family going along with that.
In the words of Matt Monro I think it's time to "WALK AWAY".
I'm sorry you find yourself in this situation and I wish you all the best for the future.
