Under Thai law if someone dies intestate then the surviving spouse does not automatically inherit everything.
The surviving spouse, as a statutory heir, would automatically receive 50% of the estate. The other 50% would then be shared by the six classes of statutory heir in descending order.
The first of these would be children who would share the other 50% equally.
If no children then the parents of the deceased would share the 50%. If no surviving parents then brothers and sisters and so on down the list.
For a full explanation
https://www.thailandlaw.org/intestate-succession-in-thailand.html