Rido & Juri

Rido and Haruka both loved Juri, so they never got on good terms because they were both rivals for her love. At first Juri was irritated by Haruka but after a while she returned Haruka's affections due to the fact that he never gave up or fought back when she insulted him, he just smiled. Rido was genuinly as fond of and in love with Juri as he was capable of and it is common for purebloods to marry their siblings. So Rido probably thought that he would get Juri and Haruka to break up and he would be the one to make a promising marriage to Juri. Only it didn't turn out that way and as soon as Haruka and Juri fell in love. Rido eloped with Shiki's mother (who happens to be a striking beauty with hair like Juri's) and then she got pregnant with Shiki then had him. Rido asked Yuki in Chapter 43: "Juri why am I not good enough?, I love you so much that I feel like eating you whole". It's unclear what kind of relationship Juri and Rido shared but it is clear that Haruka had to protect Juri from Rido constantly. Rido seemed to be obsessed with Juri and its clear that he lusted after her. It appears that in chapter 62 Rido's motive for reawakening ancestor Kaname was that so Ancester Kaname would wake up so weak and lunge at the first thing he saw. Rido knew that Haruka would be looking for him so he planned for Haruka to see the remains of his child and attack Rido in rage. But Rido would push him near the ancestor close enough for the ancestor to devour Haruka become Rido's slave so Rido could become head of the family and take Juri for his lover.