a re-entry permit wouldn't mean another Visit Thai Family if one had been obtained previously on the initial Non-O or on one of the subsequent 12 month extensions. Effectively it is one per visa.
Those that say it is difficult are trying to steer you down the agent route which the majority of people do not use because, as you are finding, with the correct planning it can be done and you get the satisfaction of doing it yourself
You need to find out from your local Thai Embassy if they issue a dependent visa for a spouse and, if so, what visa you need to apply for (probably a Non-OA) to get one. You then decide if that's the route you take and get married.