I'm going to tell you how to get Nami, Muffy, Celia, or Lumina to marry you!!
Nami: Give her skulls or bones, and Trick Blue flowers, it's the only one she'll accept!
Lumina: Give her any flower or Moon Ore (from the dig site), to win her heart you must do it every day
Muffy: Give her coins (from the dig site) and any flower, don't show her your tools, she hates them!
Celia: Give her any flower and fresh produce from your farm, she accepts only tomatoes and melons.
I also suggest to never give away your blue feather. Let them come to YOU! Oh, and when you get a girl to a pink heart she'll come to your farm and ask you questions, give them a nice answer and you'll gain a heart. Good Luck!
Submitted by Midnight Retriever