There are basically 3 levels of "title" for real estate.

Sor Kor 1 (what you're talking about) - this land shouldn't technically exist anymore. In fact, when we do land due diligence, we trace the land title back to the sor Kor 1 to ensure nothing has been issued illegally.

Nor sor 3 Kor - this is the certificate of land utilization which is akin to ownership and can be freely transferred. The land department has a mandate to convert all of these to Chanote as well but it's a much slower process. If you have this land, you can upgrade it to Chanote, usually over the course of a few months to a few years, depending on ... Things.

Chanote - this is freehold title that everyone wants, not much different from nor sor 3 Kor in practice but a bit required for most investment grade assets and people prefer them. I think transfer may be easier but not sure.

So I would double check this sor Kor 1 at the local land office to be sure it hasn't been upgraded to nor sor 3 kor or even Chanote. It sounds a bit odd to me but if it's in a rural place perhaps they're behind the times. There should be a process to upgrade, if so, have them follow it before you give a dime.

Also note you can't own land. Which I'm sure you know. If you're actually married to your wife, then you will have to waive any claim to the asset as marital property upon transfer at the land office. Which means that you can't seek a return of your investment should shit go south in the marriage. Post-nuptial agreements are voidable at the option of either party for up to one year after they're made so forget about a lam agreement.

Http://samuiforsale.com is a great resource