NO, again YOU can NOT cancel a VISA only a judge can give out a court order to cancel a VISA.
a student NEED to cancel his Extension of Stay based on education when the student stops the course or stops visiting the school. He might go on short leave abroad with permission of the school and a re-entry permit, during that short leave there is no need to cancel the Extension of Stay.
You can not pre sign all the documents, the copies of ID card and house papers from wife should be signed by her, the copies of marriage certificate and kor ror 2 by both.
You applied for an annual Extension of Stay a couple of weeks later than arriving in the first week of may. Did the Immigration Office made the 90 day report, to get you into sync with your annual application. Check the dates as a few weeks after arriving somewhere beginning may could be less than the 75 days to report 15 days ahead.
As long as you wait for your Work Permit you can not get any Extension of Stay based on Employment. Talk to the Ministry of Labor and ask them why it take so long.
By the way, working without this Work Permit is officially not allowed, be careful.
Yes, when the visa expires and you still have a period of stay or you apply for the 1 year Extension of Stay you need a re-entry permit, single cost 1.000 Thb multiple cost 3.800 thb and these will give you the same last date as permitted to stay on entry.