Hey, It is a little bit hard to understand the context here. Normally a Phrase like "So natürlich ist das doch nicht?" After someone said "ja natürlich" would imply an ironic undertone from Person A. Because Person B makes it sound like the thing that he/she is married should be obvious to everyone. Therefore he/she says "yes of course", impling "naturally, obvious i am." But Person A didn't think this was obvious, so he made an ironic/sarcastic comment by saying. "It's Not that obvious"(*imagine sarcastic voice)(that you are married) <- implied. Hope you know what I mean.