Mutual Account
Here is a variation. My wife and I have mutual account so both Diamonds with 1 account number, me primary.
I have booked 2 rooms at Hilton Sorrento, 1 in my name and 1 in my wife's name, both listed as Diamond. I expect both rooms will receive Lounge access. Upgrade is always based on availability so we'll get what they give us.
However, I expect that I will have to fight HHONORS to receive stay and night credit for both rooms, since 1 account number can only receive stay and night credit for 1 room on the same night.