Do you need to fill out special forms if invited to stay at a friend's home in Thailand?

@Brandon ***********

as per my comment above I concur that there are highly unlikely to be any problems, particularly if the guests are staying somewhere else before and afterwards so on the system for their stay, but it is not impossible by any stretch. People have been found out as living somewhere where they aren't registered under particular/unusual circumstances and fined (as a somewhat extreme example, the former British Ambassador of Burma was jailed for this offence by the Junta as Burma has similar rules on registration to Thailand, as do most Asian countries, albeit with far more draconian enforcement)