Need advice for my foreigner cousin

My cousin(13M) is Taiwanese(raised there) and moved to Singapore with my aunt (born and raised in sg) He moved back in early January but still doesn’t have a school. He couldn’t get into secondary schools and the VP of a school he tried to get into suggested that he go join Primary 6 because his English is too weak. My aunt believes that joining P6 will be too stressful for him and is considering the Admission Exercise for International Students(AEIS) which will only be at September so she dk what to do and both of them are hella stressed. Thoughts?