So sorry you're going through this OP. However, you are going to have to grow a pair of steel balls. It is highly unlikely he would be awarded full custody of the children, rarely are they removed from their mothers.
Firstly, I would contact Women's Aid and seek advice from them. They are wonderful and will be particularly useful if you are in an abusive situation (financial abuse, coercive abuse, emotional abuse). Secondly, Rights of Women is an organisation that can offer free legal advice, however, they are very difficult to get through to and persistence is the key. All information on their website. It is not true that all solicitors will give free advice initially, you will probably be able to find one but I would suggest that you need a bit more than that given the current circumstances.
Gather what financial information you can. Get a copy of your marriage certificate. It may also be worth registering an interest on the family home with the Land Registry (if you are not on the deeds). It is all very well your husband threatening you and ranting at you, but I am afraid the law is the law. He can't dictate how that works and he can't influence legal proceedings however much he thinks he can.
I undertook my own ancillary relief proceedings and represented myself due to the financial situation that I found myself in when my husband left. He had literally cut off everything and even stopped paying the mortgage. I found myself with no money and on benefits overnight and like you was a SAHM to a 2 1/2 year old (at the time). My husband mistakenly believed he could manipulate the situation and the house would be sold, blah blah blah. He ended up with zero, zilch, nothing. I walked away with 100% of the marital assets and a joint lives nominal order. It can be done.
I felt as frightened as you did at the beginning. I haven't read the whole thread but if you have RL support, please gather them round. Keep a diary if you can of behaviour. Keep notes of every little thing you can think of in terms of your husband. It sounds dramatic, but it's very important.
There are lot of experienced posters here, many who have been in your shoes. Please keep posting.
Good luck 