I’m quite late to the party, but while searching for details around splitting a PNR I came across this thread and was shocked (Shocked, I tell you!!) to see that no one called this comment out as incorrect.
It’s my understanding that medallion status is determined by the highest level on PNR’s of two or less people, but on three or more, the status is determined by the LOWEST status holder…
In this case, isn’t the OP trying to split off because they know that they’ll be dragged down by the lowest status carrier in the group and they’re trying to avoid that specifically?
I’m booking reward flights for my family of three and I typically book myself, my wife, and my under 16 son with points, then split out my son and I (I’m diamond), and keep my wife, whom I gift gold, on her own. In a pinch, they can “steal” my seat if only my boy and I get the upgrade (I’m an old fashioned chivalrous gentleman… lol) and I can take her seat in main.

Am I making a mistake?