You may not love your characters but you do have to defend them. Our characters arise out of our need for them.
Always look for something you can identify with in each of your characters, good or bad. Always look for something honest. And then, once you have the perfect cast, the story will virtually write itself. Now the most important work is done and the fun can start.
It's time to play.
More than any other quality, contrast defines characters. By contrasting two characters, the strongest character dynamics are achieved. Almost any relational story that comes to mind, whether a romance, a partnership, or a friendship, probably contains contrasting characters.
Keep the association between characters tight. Ensure they need each other for things to work. Change the emotions of one of the characters. What piece of information (truth or secret) could cause problems?
A good story happens when you get your character down that blasted rabbit hole. The plot is just a vehicle for the characters. When they are dealing with problems, they have to reveal themselves for who they are. Just keep them moving and let them bounce off each other.
Start now. Don't worry about the past. Flashbacks should set off alarm bells that there is something not quite right with your story. Instead, think of Lewis Carroll’s ‘Alice in Wonderland’. By the end of page one Alice is down the rabbit hole.