PNR is the reservation, DM is DM. Different beasts. Pax are linked (to the status of the highest Pax) on the PNR but not the DM.

That being said. I have seen:

JONES/Mr
SMITH/Mr
JONES/Mrs
SMITH/Mrs
SMITH/Jnr

Become

JONES/Mr
JONES/Mrs
SMITH/Mr
SMITH/Mrs
SMITH/Jnr

right before my eyes on the screens during DM UPDG processing. Perhaps due to a member of one or other SMITH or JONES parties telling the GA they did not wish to be split up. So in this situation I would tell the GA you are a party of two, smile and see what happens.