Can a Fijian passport holder obtain a visa on arrival in Thailand a second time during the same trip?

Hi all, we are going to Thailand and Vietnam for 6 weeks flying from uk to Bangkok airport. Myself and our two children have British passports and my husband has a Fijian passport.

I understand myself and kids will get 30 day visa exemption. And my husband can get a 15 day visa on arrival.

So our plan is to stay in Thailand for 15 days then fly to Vietnam for two weeks. Then fly back into Bangkok. My question is will he be able to get a visa on arrival again? Our main return flight is uk to Bangkok so we do need to enter and return via Bangkok. We are just about to book our flights and I’m feeling so stressed now about visas! 😭😭 thanks in advance for any advice fellow travelers