Apply for a UK tourist visa on the gov.uk site. You will need to put in all their parents and kids details in full. Chuck in your bank statements showing you are financially sound, put all their bank statements in as well showing all sources of income. Any transfers from abroad such as via Western Union should be shown, print them out and submit them. If they work you will need to show wages into bank , working and paid in cash not accepted. All applicants have to have biometrics in Bangkok , you can turn up with them but they be by themselves at final submission.