I need advice about legal documentations! Please help!!!

I am 18 years old and is a Canadian citizen.

I am currently in Vietnam for the summer and would like to bring my 12 year old brother (also Canadian) and my grandparents (Vietnamese) to Bangkok Thailand for 5 days for tourism.

For my 12-year-old brother:

Are any parental permission documents required for him to travel with me?

If so, must the original signed permission letter be presented, or would a scanned/digital copy be sufficient?

Is a birth certificate or any additional documentation required for him as a minor?

Visa requirements:

Do Canadian citizens need a visa for a 5-day visit to Thailand?

What are the visa requirements (if any) for Vietnamese citizens traveling from Vietnam to Thailand for tourism?

Hey everyone I’m a Cambodian citizen currently living in Bangkok Thailand was planning on going to taiwan does anyone know where I can apply for taiwan visa?