Previous advice given here was that my Brit wife can apply basically at the same time as myself (at Chiang Mai Immigration). I have since read reports of there now sometimes being delays in having an annual extension application approved and wondered if such a delay would hold up the dependent's application? Maybe both applications are bundled up and processed together? Thanks.

I have seen no reports of extension approvals being delayed in CM.

In reality the a dependent extension cannot be processed until yours is completed. You can have the application form completed and required documents attached with the exception of your new extension stamp. As soon as you have the stamp in your passport you have to make a copy of the stamp to do the application.