that's identity theft, consequences i can name a few like your sister can't use her real name, in some countries, there is such thing as iris scan, so if you are using your sister's id and your iris is scanned then your iris will be recorded under your sister's id, your sister can't use her own identity and you can't also, in some countries, it entails 3 to 6 years imprisonment, it is a serious offense and far more greater consequences in the future...