Hi Addis,
I guess we both submitted our application same month (September) it's just that we have different cases. As far as I know DNA test is only applied for the children of applicants and reference person (proof that the child is really the child of the reference person in Norway).
Embassy haven't interviewed me or my fiance either. With the first email that you have recd from UDI, did they mention the time frame as to when are they be having the decision?
I have a friend who is married with a Norwegian and they have a kid. they submitted their application Feb 2014 and til now they don't have yet their residence permit. With your case, Im sorry i cant answer and I am also wondering why its taking 20 months processing.
Let's pray and be patient that we will recd our visa the soonest possible time.
Will keep you posted