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With the correct documents and your Thai wife...sixty.

For the extension in Chiang Rai they require the following: Tm7 application form + 1 photo

Passport and copy

Visa page copy
,Tm6 entry card in passport,copy
wife ID card, copy
Wife housebook, copy
Marriage certificate, copy
Kor ror 2 form - can be obtained at the Amphoe office for 20, baht 
1900 baht

“...my daughter will be 18 (eighteen) in March.”

Follow the protocols if you have concerns is a good idea.

Also check the Popular Topics above...much useful advice about embassies and consulates.

Consider your budget, know the locations of Thai Embassies and Consulates, check transit options and hotel prices...go where you might see something different with the required documents and try to travel back in at a land border.

Also, make sure the embassy or consulate is open on the dates you want to go and if an appointment must be made prior for a specific date.

@Ian ********

Autodidactics

They are the best advisors on-line, my time at the Thai Consulate there was easy because of the advice I received.

I wish my airline travel had been as simple.

The whole thrust of current enforcement on using exempt entry or tourist visas to stay long term, seems to be the desire to get those that can stay long term onto getting those visas that allow them to, and limiting those that don’t want to or can’t qualify for longer stays.