You understand, I think, that this man is abusing you?
Abuse tends to escalate during or after pregnancy because they feel confident they have you too trapped to attempt to leave. Marriage causes the same issue. It's about power and control, violence only features as a means to that control where other tactics have not had the desired effect (from their point of view).
Ultimately I can only tell you what I would do. It may not be what you would do.
I would not want to legally tie myself to a man who was already abusing me (to quite an extent), especially where I was also already aware it was abuse.
I would be extremely concerned that his only reasoning for initiating marriage himself would be to tighten the noose and gain even greater control of you, and feel entitled to treat you even worse. This is usually why abusive men push for marriage. It actually frightens me for your safety.
Once married the only way you can extricate yourself from that is through divorce, which will still take years even if he agrees to it. Let's face it, he's unlikely to do this given how important it is to him to have control. Dragging out divorce as long as possible, and hurting you as much as possible along the way, will be more ways for him to have power and control over you. He's not going to agree to split his assets with you willingly, or be reasonable.
I don't know where you'd stand financially if you divorced him rapidly after marrying. But if you instead stayed with him for years, can you imagine how much he will have broken you by then? Or if you'll even have the strength left to try and leave?
I understand why you'd consider marrying, and I've seen it suggested here often enough, but I'd be seriously worried about you if you were a friend of mine telling me you were considering it in these circumstances.
If you instead left now, yes it would be difficult for a while, but you'd also be able to start rebuilding immediately. You'd be unchained from him immediately (children aside). You'd already be on the path to a better life, and you wouldn't have potentially years of legal wrangling through divorce ahead of you.
Marrying now would just delay the possibility of leaving until he's inflicted more damage on you (including restricting your job prospects further) followed by a protracted period of trying to get free of him.
Is part of your thought process the hope that marrying might fix things? Because if so, whilst totally understandable you would feel that way, it's really not what will happen.
I would leave now, and keep my eyes firmly fixed on the better future I was building for myself and my DCs. I would also stop blaming myself for his behaviour - we don't see it coming, otherwise they'd never get close enough to get their claws into us if they weren't convincing actors. It's not your fault.
Freedom Programme could help you get some clarity on what's going on. They won't judge, it's confidential, but it is worth your time: www.freedomprogramme.co.uk
My life is unrecognisably better since I went on FP and then left - and better in ways I couldn't even have imagined back then. Yours could be too. I don't think marriage will do anything except make all of this worse and more difficult, so for that reason I really hope you feel able to leaver sooner rather than later and are able to make it happen.
Take care 