The wife and I want to relocate to Bangkok. I have had a retirement visa in the past so I know the ins and outs of that. But is there anyone who can give some advise regarding getting my wife and my step daughter (15 years old) non-immigrant visas? I imagine this has been discussed but I wasn't able to find anything exactly on point especially regarding the step child.

Normally this is done when you have here on an extension of stay and they obtain non immigrant O visas on that basis and relationship to you and can then enter and later obtain matching extensions as dependents.

I suggest that all of you get single entry non immigrant O visas before departing. You would get it for being over 50 and your dependents based upon yours. If you don't get them your dependents would have to make a trip to a nearby embassy or consulate to get their visas after you get your extension.

If there are any honorary Thai consulates where you live they would be the best choice.