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.