Phuket is a famous tourist attraction. I think they can enter to Thailand under the visa exemption rule. when the immigrant officer asked their purposes to visit to Thailand, please tell the the office that we would like to visit Thailand as tourism purposes .
Under this rule provided that they meet the following criteria:
1. They must have a confirmed return ticket to show that they are flying out of Thailand within 30 or 15 days of entry, as appropriate. Open tickets do not qualify. Traveling over land out of Thailand by train, bus, etc to Cambodia, Laos, Malaysia (including en route to Singapore), Myanmar, etc is not accepted as proof of exiting Thailand.
You may be asked to show your flight ticket on entering Thailand. If you do not possess a flight ticket to show you will be exiting Thailand within 30 or 15 days of entry you will be most likely to be refused entry.
3. It will also be necessary to prove that you have funds of at least 10,000 THB per person during your stay in Thailand.
A fee may be levied on persons entering Thailand under the VISA EXEMPTION RULE.
Whatever if they would like to apply a business visa, I will prepare an invitation letter with the supporting documents for them.