TAG is an automatic program, if he meets all the requirements he will be accepted via TAG. Print out the pdf given earlier and go thru it line by line, checking off each as you are sure they are met. The toughest hurdle is likely the requirement he must have 30 UC-transferable semester (45 quarter) units completed by prior to TAG submission, this is the AP credit plus any classes he takes at a CCC this summer.
A bonus of the 1-year transfer is it appears he can spend 3 more years at the UC since they say
Students who enter UC with AP credit do not have to declare a major earlier than other students, nor are they required to graduate earlier. AP credits | UC Admissions
As explained by @Gumbymom the other UCs may be more difficult for non-TAG admission after 1 year because he won’t have much of a record for them to judge his college performance. So while the only penalty for applying to them is the time spent on the applications, I’d put most of my hope in the TAG application.
He may want to read thru a post I wrote a while back suggesting students interested in transfer to UCSB attend community college at Santa Barbara City College. The post is at https://talk.collegeconfidential.com/t/backdoor-way-into-ucsb-2025-version