Thanks. Yes, you get an Embassy letter if you renew a UK passport in Thailand but if you do it in the U.K. you don't. She won't get a letter in Laos, but hopefully that won't be an issue.
When I moved to a new condo, I didn't send off the TM28 form to Immigration until about 3 months after I had moved in. There was no issue; they just returned the slip.
If your employment is secure, is there any benefit of transferring him to an Ed visa, rather than remaining as a dependent piggy-backing on your work extension?
Thanks. Then presumably at passport control at the airport in Bangkok we just show the Extension stamp and Re-entry permit in the cancelled passport? Then get them transferred into the new passport later?