I got my dtv in hcmc then applied for dependant in Taipei in December before everything was online, so I'm not sure if this is still helpful
I only provided 1 month bank statement with 500k thb that was in it for 3 weeks. I included a sponsorship letter stating I am responsible for their accomodation, spending and any other financial expenses.
The usual documentations eg passport, copy of my dtv etc
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