@Waffletots your strength and resilience is absolutely astounding and you are a credit to yourself. I read your post last night and was absolutely gobsmacked at his deceit and lies.
I would only hope that I would be able to handle anything like this as well as you have, notwithstanding your current situation of being heavily pregnant.
Please take all the support offered to you over the coming days, weeks and months and don't think for one second that you owe him anything at all.
His silence is deafening, and he will have to deal with the consequences of his actions. You sound like you are an inherently good person and your children will benefit from this - you've already demonstrated putting them first in all of this, which is commendable.
Your parents and brother sound very supportive too, you are lucky and you will need them over the next few months.
With regard to finances, access some advice when you can and in the meantime I would not suggest emptying the joint account if you can afford to leave it there. No doubt you will need to consult solicitors at some point and by leaving everything where it is for now, again you're demonstrating your credibility and prioritising keeping a roof over your heads.
I will look out for your updates and I wish you lots of love and strength over the coming days and weeks - you have definitely got this and you will come out of this a stronger and better person.
Try to rest and sleep as you can x