Thailand does not have a gift tax that in other developed national economies is used to prevent avoidance of an inheritance tax. Furthermore, I believe the Thailand inheritance tax only applies to "registered" Thai assets. Foreign property is not "registered" Thai property. Obviously, in Thailand there is a big loophole for the wealthy in wealth transfer, albeit a legal loophole.
But note there was a similar issue regarding PM Prayut's sale of property originally transferred to him as a child by his father. Prayut's response in 2014 was:
"So what's the deal?"
So I repeat.