@Wilson ****
Besides the Non-O Visa based on being former Thai Citizens, they can stay in Thailand using any visa or extension of stay that they qualify for.
They can go through the following websites:
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and
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and see which visa they may qualify for to enter.Each embassy may have slightly different requirements.
They may be able to get an extension of stay, if they qualify for an extension of stay.
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*****
Each immigration office may have slightly different requirements.