if you are a Thai citizen and you have a child born for example in the USA and then you register the child also as a Thai national will that put the child into the military service lottery?
that is exactly what I would expect the sales person to say, definitely check with local immigration and with a reputable visa agent or two, there should definitely be a way to stay.
If the owner of the property has not filled in a TM30 for you at that address they are liable for a fine, you maybe asked to pay the fine on their behalf at immigration.