There are a things you say you'd be doing if you gave this man the boot, and they're just not true.
You wouldn't be breaking up your family and you wouldn't be depriving your youngest of her Dad, those things are solely down to your DP deliberately choosing to act like a total wanker whenever he's around your beautiful, vulnerable DD1.
It's difficult to drastically change your home life to a place where your DD is safe and protected from this man (I know because I've had to do it myself), but you must do it, you have no choice.
The thing that I kept repeating to myself is that sinister line abusive people always come out with to shift responsibility for their behaviour onto their victims - 'Now look what you've made me do...'
She doesn't make him do it, he's an adult and fully in control of his own behaviour. Proof of that is that he wouldn't act like that with his boss/mates, and you've said he's fine with your youngest (who is pliable and won't challenge him at the moment, but be assured, he'll be the same with her when she's older and can).
How would you feel if it was another man treating your DD like this? Would you even hesitate to defend her tooth and nail?
If you would then please do her the courtesy of demanding respect for her in her own fucking home!
Let this drop and you will fail your DD.
(Apologies if I'm repeating pp advice, haven't been able to read all the replies)