I think that there is a connection between (sugar and monet) and clover.
First Oda has told us that sugar and monet are sisters. Second they joined the Donquixote Pirates after they were rescued from a terrible tragedy by donquixote doflamingo, then gained their devil fruits.
So "Why" did doflamingo rescue them. -- They must have had some importance.
First lets look at symbology
Monet has been seen with books about astronomy -- clover had a solar system model
Both Monet and Sugar have green hair -- Clover has green hair
Sugar works under Trebol who has the clover symbol to represent him -- Clover's (name and hairstyle)
Monet's fruit is named the yuki yuki not mi. Monet is representive of a yuki onna. A yuki onna is a snow woman. She can represent Mother, Daughter, Sister, Lover .... We have seen her as a mother figure with the children, but we could also think of her as a daughter to Clover or a sister to Sugar. The story below is from http://hyakumonogatari.com/2013/12/18/yuki-onna-the-snow-woman/
"No one knows exactly where Hearn got this version of the Yuki Onna tale. People have searched for years to find the original, but without success. According the Hearn’s preface, it was taught to him by a local man. Researchers have tracked that down to a potential candidate, a father and daughter who worked as servants in Hearn’s house in Tokyo. The daughters name was Ohana, and the father was Shuya, and they came from the Oume district of Toyko. That area has some similar folktales, which make Ohana and Shuya good candidates."
Ohana sounds like Ohara. And this yuki onna story is about a father and daughter.
Donflamingo has blackmail on the Gorosei -- Clover knew too much about the void century (maybe more) when he spoke with the Gorosei before his death
Also in the anime Clover is refered to as professor, and seperately has a title of authority of archaelology. It would be illegal to transcrible the Poneglyph. So would he really be a professor of archaelology? I think he would have been a professor of astronomy. Also the Gorosei said before Clover died that they knew his name well. It could have been that he was known for other things.
So my theory is that Clover is Sugar and Monet's father. I think after the Ohara incident Clover's family was in danger. The world government ordered to kill them too. Donflamingo saw an oppertunity and rescued them in order to learn something about the world government. Monet knows something about astonomy which is important, but not about the void century. That information is still valuable to donflamingo. To prevent Monet from ever betraying Donflamingo he keeps sugar by his side.
Does anyone think that it is possible. Support, Rebuttal