Tricking or coercing someone into sexual contact (especially at that age) is definitely a from of molestation.
Whether or not you want to go to the authorites about it, well, that's up to you. Many cases of rape and molestation go unreported, and that's really something you need to decide. Especially with issues regarding family and close friends, it really isn't worth it to press charges. If you feel that you need to go to the authorites for closure for this situation, then more power to you. But that is by no means something that you HAVE to do.
Whether or not you want to go to the authorites about it, well, that's up to you. Many cases of rape and molestation go unreported, and that's really something you need to decide. Especially with issues regarding family and close friends, it really isn't worth it to press charges. If you feel that you need to go to the authorites for closure for this situation, then more power to you. But that is by no means something that you HAVE to do.