You will have a good idea of what you can cope with re moving out/staying in your home. I trust you when you say it’s safest for you to leave and then deal with everything from a place of safety and with the support of your friend.
Can you start moving things out bit by bit.
I’d get all your documents in order first, birth/marriage certificates, passports, financial papers.
Then focus on what your kids need - anything precious to them and anything they need for sleep eg precious cuddle toys and pjs etc.
Then what you need - anything sentimental, clothes, comfort items, things that help settle you and help your well-being.
Change passwords on all email account, bank apps, shopping apps etc. It may be helpful to have a clean, new bank account and email address. The day you leave start an application for universal credit using your clean email and bank account (if you don’t already have a claim in - if you do change your email and bank details on there).
Redirect your mail to your friends house, use the clean email address as contact details so confirmation doesn’t come to the house.
Check your phone, electronic goods, and any apps to ensure there aren’t tracking apps/location services on there. Also consider a new mobile number/phone, transfer all your contacts onto the new phone so you’re not worrying about him phoning and harassing you. You could block but having a number he doesn’t know might be quite liberating.
Let the police know you’re fleeing domestic abuse in case he contact them saying you’re missing.
Let school know you’re separating and fleeing abuse, they can’t refuse to hand kids over if he has parental rights, but if they know the background they can disuade him/contact the police if he does appear.
Its a very scary time but you can do this, wishing you courage and good luck.