You really need to ho onto the Thai Embassy website and read ref Visas, you really need a tourist visa 60 days and then apply for 30 day extension at the local immigration office, do not overstay your 60 days.
I would reccomend Kuala Lumpur, whe I applied for a further tourist visa a few years ago the process was very easy, but remember you do not get the visa until 9am following the day you apply.
You should have said that in your initial post ! Well he needs to get the right visa then, go on to the UK Thai Embassey Web site, marriage visa, I think everyone assumed he was 18 !