If you read Chinese, Chinese instruction might be more clear.
https://www.immigration.gov.tw/5385/7244/7250/7281/定居/36430/
no, but they should be in Taiwan at least for a few days. They just write the parents or grandparents address of household registration on the form, and they can apply for residence certificate from overseas, but should receive the residence certificate in Taiwa, then should apply for their household registration at HHR office. The processing time is 3 days or so.