I fucking love dogs but this one must be PTS - it's a large dog with the power to easily kill a human, which has bitten twice drawing blood, and is displaying other aggressive behaviour.
Do you feel confident that your husband will not hurt you if you do this? If you are certain he won't, it's a no brainer and you should do it tomorrow. If you have any worry that he might, you need to speak to Women's Aid and leave with your children, ASAP.
I sorry I am being brutal, I know it's not easy to even contemplate leaving a man you love, but your children are at serious risk of life-altering injury/death. As it is, living with an animal like this must be destroying their mental health, and yours.
And you need to try to understand that there is nothing remotely normal or good about a man who insists his family, including his small children, live with an animal that can and may kill them. Not to mention the untold mental suffering he is happy to inflict on you all on a daily basis by keeping the dog. What was his reaction when the dog drew his children's blood?
He either has extreme cognitive challenges, if he is genuinely unable to comprehend the threat and the damage, both physical and mental. In which case, it's hard to see how he can fulfil the responsibility of being a father in a way that is safe, so you need to protect the children from his dangerous incompetence.
OR, he has an almost psychopathic level of indifference to the suffering of others. And you need to protect the children from his malice.
Either way, you need to somehow find the courage, with support if appropriate, to do what it takes to protect your kids from the dog and the father.