The third team I keep thinking of is the Knicks if they start losing. Carmelo to the Kings, Cousins to the Celtics and a collection of Lee, a young player (or two) and (non-Net) draft picks going to NY and Sac.
The Kings get their wish to keep "trying" to make the playoffs now. The Knicks get help rebuilding around Porzingis. Celtics use many of their assets to get a star.
Though for this to happen, the Knicks need to start losing at a higher rate and the Cousin King issue must intensify. Plus, there must be at least one asset the Celtics have that the Kings want to go with Melo.
I actually think it would be more likely that Cousins goes to NY and Carmelo goes to Boston with the Kings getting young pieces and draft picks. That actually seems to make more sense.
Something like (other pieces could be included)
Boston - Anthony
NY - Cousins & Gay
Sacto - Lee, Bradley, NY 1st, Dal 1st, Minn 1st, Bos 1st
That seems fairly reasonable for all three teams. Plus, I don't see Melo willingly going to Sacramento, but could see him willingly go to Boston since it is so close to where his wife wants to be.