The difference from years ago is that a PNR is split only if you get upgraded within 24 hours. Before that either you both are or both aren’t.

in theory your spouse should retain their position on the list, though that doesn’t always work. Sometimes they’ll fall to the bottom of the 1K list. Sometimes they might fall off (as GM) or to their status level.

if the return is a different PNR - do you book two one ways?