Sure, the Weasley twins may fall under Aries only because they were born on April Fool's Day (the most appropriate day of the year for the prankster duo); but Aries are full of confidence and ambition. They know what they want, and they're going to do whatever they can to get it. Aries are self-assured, passionate, impulsive and in some cases business savvy.
There was never a moment that the Weasley twins doubted themselves or let others deter them from their goals. Also, there is the irony that Aries is opposite to Libra, the sign of partnership and balance
Horace Slughorn & Pomona Sprout - Taurus
Taurans live by the motto, "work hard, play hard." They have a taste for the finer things and like to indulge in their pleasures - food, coffee, alcohol, sex - but only when it's earned. Horace Slughorn loved surrounding himself with successful people and throwing lavish dinner parties for his esteemed friends.
Pomona Sprout was also a Taurus, demonstrating the other side of the zodiac sign's coin, valuing hard work and encouraging her students when they showed promise. She was a firm yet maternal figure, with an affinity for gardening.
Draco Malfoy - Gemini
Gemini, The Twins, are multifaceted chameleons who assess social situations and choose their appropriate masks. Some may be quick to label Geminis as two-faced and fake, but at their heart, Geminis just want to belong - preferably to a group they deem as cool or of respectable standing.
Dudley Dursley & Dobby - Cancer
Cancers are homebodies who love spending time with family and friends. Dobby deeply cherished his friendship with Harry Potter, always going above and beyond to help and show his love.
On the flip side, Cancers can be moody or "crabby", something we definitely see in Dudley Dursley. He loved his home comforts and being around his Petunia and Vernon Dursley, who always pampered him. Dudley was also prone to nagging and sulking when he didn't get his way.
Harry Potter, Ginny Weasley, Neville Longbottom - Leo
Leos are natural-born leaders, divas, and heroes. Which makes perfect sense for Harry Potter, Ginny Weasley, and Neville Longbottom.