Goodness, I have just RTWT.
OP you have had problems in the past with your ex, and then he became nice again and persuaded you to stay. You had problems and then you fell pregnant. You had problems and then at Christmas he was all nice and proposed.
There is a pattern, Sweetheart. When he has been violent or abusive and you are considering leaving, he becomes nice again - the man you fell in love with - long enough to reel you back in. Abusers are often nice people, loveable, charming, persuasive. It's why we fall in love with them, and one of the ways they maintain control.
Your dcs need you, and they need you to be with someone who respects you, who listens to you, who does not put you down, threaten or attack you. He may have rights to see his child so if he has changed, that's great. He can use his new found kindness to build a positive relationship with his child.
No-one should have to be spoken to, and treated as you and his dc were.
No-one should have to live like that. For him to want to change, and become a decent father, will take years of work on his behalf.
On average it takes an abused woman 7 goes to leave a violent partner. You left a few days ago, then the police let you back in. You said then, I wish I had stayed away. He will be nice to you now, but if you went back, you have lost all of the opportunities you have taken this week to take control of your life.
Think about your two babies. Do you really want to move them again to a remote village miles and miles from your dad to risk it again. If your stbx really wants to be close to you, he could move nearer to you, letting his baby see him occasionally. You do not have to go back to the middle of no-where, and put yourself back into his hands again.
Thinking of you.