Sorry I haven’t posted in awhile, been busy with school :(
1- Assuming you are in the same situation as Yui and are around them on a day to day basis, I’d say it would take about five to six months for them to form a crush or an attachment towards you, albeit twisted. As they all struggle with the understanding of love and find it difficult to maintain healthy relationships with others, they will act on their crush in a destructive and violent manner. Their pride, sadistic natures, as well as the need to maintain the ‘predator’ status also make it difficult for them to treat their crush in a healthy way. Despite the attraction it will take many more months, if not years of constant compassion and support for them to have a healthy, and positive relationship with each other.
2- Honestly, I think it would take a few years for them to go from crushing to loving. Similar to Yui, their crush will need to act as a constant source of support and attention towards the boys. These boys are lonely, and love starved. While the support definitely helps, it takes a lot more than kind words to reverse years (centuries, maybe) of neglect and abuse.