Sherry and Grace are loversThis theory isn't based on any hints between the two in dialog, but their vast mismach in skills. Sherry is fairly competent among the AI golfers, but Grace is completely inept, even among the AI golfers. The reason they stay together is obvious.
Alternately, Grace's parents pay Sherry a lot of money to keep her aroundMario wiki mentions she is spoiled going by her Japanese profile.
Azalea is Daisy's alter-egoWell, both character's have similar stats, share the same colour scheme of orange, yellow and white. Also Daisy's current design bore a resemblence to Azalea's back style. (Unknown if her bangs were hidden behind the hat or that was cut at the time.) Her tan most likely faded away after appearing in Mario Tennis and Mario Party 3. It would be possible that when Daisy was caught, she dropped the second identity, possibly explaining how Azalea never appeared in another game.