have recently discussed this with Immigration. The answer is quite simple, at this time, subject to change you put into place a power of attorney for either next of kin or a law firm, you will also need a letter from a registered doctor stating the medical illness leading to the inability for the Visa applicant to attend immigration in person
The letter from the doctor should state clearly that the applicant is incapable of attending in person and the reason why, that will then give the holder of the power of attorney the ability to approach Immigration and deal with matters on the applicants behalf. This is as we all know Thailand and that is the advice that we have at this time but this can change. I hope this helps everyone with an interest in this area. 
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