Have him check in with the Condo management. It is their responsibility to report foreigners to the immigration even though they often neglect it. That is all he or you can do.
Schedule enough time of jumping to the hoops of the paperwork in Thailand. Getting your translations certified by the Ministry of Foreign Affairs (you need to make an appointment online) will take at least a few days if they are happy with the translation. If not - redo and add other days. As for finding an appointment at the Amphoe - we had to show up to get our documents checked and only then we received and appointment to come back - three weeks later. This might be different with other Amphoes outside Bangkok but the bottom line is that you need an extended period on your visa. Good luck
Update: No online appointment = no service. Do not waste your time to come here as a walk-in. Many frustrated foreigners as they were not aware of the online booking requirement and there is no information on the Website of the MFA.