I’m really sorry you’re going through this. But the most important thing right now is to stop trying to make sense of his contradictory words and start dealing with what he is actually doing.
He may genuinely still have feelings for you, but saying “I love you” while also saying he wants to move on, date other people and possibly remarry tells you that he is currently choosing to end the relationship. Trying to work out how he can love you and still do that will keep you trapped in a loop. People can still care about someone and nevertheless decide they don’t want to continue the relationship.
The WhatsApp blocking is different because you have children together. He is entitled to create boundaries around personal conversations, but you both still need a reliable way to communicate about your daughters. I would stop contacting him about the relationship and send one calm message by whatever other method is available—text, email, etc.—saying that you accept he wants space, but you need an agreed channel for essential communication concerning the children.
For the next few days, focus on practicalities rather than the future he is talking about. You do not need to process him potentially remarrying or having more children when the separation has only just happened. Those are hypothetical future events and thinking about them now will only cause you more pain. Deal with today: where the children are staying, finances, bills, childcare, contact arrangements, access to the home, and how you will communicate.
Also, don't beg, repeatedly call him, monitor whether he is dating, or try to persuade him that he still loves you. Not because you shouldn't care, but because right now it gives him control of your emotional state and usually makes the person who has left withdraw further. Give him the separation he says he wants while protecting your own and your daughters’ position.
And please get some support around you even if you feel you have nobody. Tell your GP how badly you are struggling, particularly if you're barely sleeping, eating, functioning or caring for yourself. You can also contact family support organisations or your local council/children’s services for practical support as a newly single parent. If money is going to become an issue, check Universal Credit, Child Benefit, Council Tax Reduction and child maintenance rather than waiting to see what your husband decides to contribute.
Most importantly: you do not have to solve your entire life this week. At the moment you're in shock. His decision does not mean you and your daughters have been discarded or that the family you have had meant nothing. But for now I would take his decision seriously, stop discussing reconciliation with him, establish child-focused communication, and start quietly securing the practical side of life for yourself and the girls.
If by “on the verge of a nervous breakdown” you mean you feel you might harm yourself, cannot keep yourself or the children safe, or feel completely unable to cope, please contact someone immediately — in the UK you can call NHS 111 and select the mental-health option, call Samaritans on 116 123, or call 999/go to A&E if you are in immediate danger.