Thailand has no anti-discrimination laws. Too short, too fat, too bald, too old, perceived disability, actual disability, skin color, etc. Superficial judgments.
Perhaps not spending enough money. Immigration might be predisposed to think that multiple back to back no-visa entries are made by those looking to live in Thailand on the cheap and don’t support the Kingdom economy. Anyone that does this is at risk for being denied entry.
It is hot. Get used to the heat. A/C in homes for bedrooms but often not available or operated in living areas. People spend time in shopping malls to take advantage of air conditioning.
You said carry on bag. Obviously, you meant a checked bag. Carry on limit is 7kg. for Vietjet. My wife and I make sure not to exceed this limit. Most international air travel limits for a checked bag is 23kg. Never expect a break at the counter. Bags get weighed, policies are in writing. In English.
You didn’t mention whether or not you have visited Thailand and stayed here for any length of time. Living here is different than vacationing here. Adjusting to the climate takes time. Sorry to go off on a tangent from what you asked about.
Definitely. They are in the US. Sell them on the benefits. Citizenship doesn’t need to be renewed every 10 years! Then they can have a US passport. Best wishes!