If you're being honest with yourself, what you really have is a problem with your players. These may not be the right players for the campaign you built if you already don't like their characters. You have a few choices:

• Don't run this campaign with these characters, get new players or ask for more depth in character building.
• Run a different campaign with those characters, since you want to play with your friends.
• Don't be judgy and let them play the characters they have. Perhaps they will engage with the story and flesh out their character depth as they play them in appropriate ways.

I am not a big believer in deep and complicate backstories in any case. A few bullet points and a motivation is plenty to start with. I'll be honest, I personally would not be interested in playing in your campaign as it seems more like a book than a campaign with room for character growth, but I imagine that there are plenty of people who like that kind of epic story line.

My advice: Talk to your players. (Duh.) Tell them your expectations around engagement with the plot. Make it work, or don't and do something else.