I’m so sorry to read you are going through this nightmare.
I’m the adult child of an abusive man and I was still living at home when my mother finally tried to end the relationship. What you have written is sadly very familiar. I told my grandparents some of what had been going on, expecting help, and they turned on me. It’s very difficult to understand if you are a normal person with empathy, but these abusive men are usually abusive due to their upbringing. So, yes, his parents are also horrible selfish people.
My advice based on my experience is to keep talking to Women’s Aid, they have a forum and online chat, too. They were very helpful to us. This might sound odd but the Samaritans were amazing as well and you can call them any time, they helped when we were feeling desperate and needed a friendly voice.
The local Women’s Aid branch was very very good, and are THE people to talk to. A lot better than the helpline and you get to see people in person who really get it. They can give advice and counselling when you are ready as well as help with essentials (at ours food, personal care items). Google Non-Molestation order and ask the branch about how you can get one of these, our knew of solicitors they could refer us to who could help with this. Start collecting evidence to support getting one of these orders. Mine stopped my father’s harassment.
Do not answer your phone to your husband or his parents anymore, let them harass you by text and email. Do not reply to any messages (easier to prove harassment this way), but don’t try to block them yet. You need these as evidence of the harassment. Print these as they come and put any emails in an electronic folder, the same with any social media messages (save and print). Make written notes of the time of the calls and what (roughly) was said, refer to your phone log.
Get evidence in the form of a bank statement to show he has cleaned out all the money from your account, this is financial abuse. Lovely bit of evidence, especially when he’s left you with the baby.
If you can get the photos of your injuries printed and backed up do so right away.
It’s a good idea to keep a diary if you can of events, both historic and recent. It will get hard to remember things as it’s so upsetting and it will help you to fight for protection. Also, call the police every single time you have any issues with him or his parents. Try to make sure they link the calls/call outs together and keep a log of when you report and what happens each time. I believe you should get a reference number each time, keep a record of these. I feels awful the first time you do it, but it gets easier.
Lots of individual complaints and call outs is better than one, it shows a pattern of behaviour and the police will also gradually get fed up with him, even if they can’t always do much. Some police will also be more help and better trained than others.
This is especially important if he turns up at your home or where you work. Do not engage with him, he is very dangerous. When you leave or end the relationship is the most risky time. Call the police, or get work to call them if he shows up there.
If you have a HR department at work let them and your line manager know what is going on and ask if there is anything your employers can do to support you. There needs to be action taken regarding your pay and putting it into a different account which he cannot access and they might be able to offer an advance to help you pay for childcare, get a new car seat, or otherwise sort out some short term support.
If your ex also turned up at your workplace you have witnesses to his abusiveness, taking the car seat, the lot. That’s worth more than this bloke’s parents word, which is clearly going to be biased. Send an email to work going into detail about the incident (just factually as possible describe what happened, be as accurate as possible) and ask if they see any discrepancies in your account, say you are making them aware to call the police if he comes anywhere near to work again. Ask if they could reply confirming they are aware of this incident, that they what you have written if accurate to the best of their knowledge and to acknowledge your request RE police call outs. Keep this email and replies as evidence, but also ask if they would mind reporting the incident to the police themselves requesting the ex is told to stay away from their premises to help you get him out of your life so you can get back to work, as this will give you more evidence of his actions and may have more weight coming for a 3rd party. They will want you to go back to work and probably to do not think much of him nor want him there, so may well be very helpful.
(sorry this is so long, I hope is all relevant and thinking of you and baby)