Changing the job - requirements for work permit and visa

Hi everyone...

My American friend who is now working for a language school  in Bangkok, he's got a new job a new public school. He has a valid non b visa and work permit from the current school. The contract for new school will start on May 15

Here are some informations he received from both schools.

- Current School: They will cancel the visa before May 14 but they will write letter to extend TR until May 14.  They asked him to return his work permit on May 14 for cancellation in the morning.

- New School: Already received all the documents for work permit and teaching license application from my friend. They asked my friend to inform current school to cancel visa and work permit on the same day. If his visa is cancelled before May 15, they won't have enough time to do his paperwork.

So, could you please advise on this? What should he do now? He doesn't quite understand the process. Although this is not his first time for job changing, it seems a bit complicated in the protocol from his current school.

If my understanding is correct, the current school just need to give him the termination letter that specify the date his job ends which is May 14 for further cancellation of the current extension. And the duty shall belong to the new school to complete the wp and other documents before May 14.

Sorry for a long story but I just wanted to make sure that all the information is included.

Thank you so much! ????