OP - this situation sounds horrendous and you absolutely can leave the relationship (and should, by the sound of it).
Insulting you, mocking you in front of other people, pinching you to make you shut up... all of these are deeply unpleasant behaviours and that's before you mention spraying you in the face with vinegar. This is an emotionally and physically abusive relationship, and it sounds financially controlling too.
With regards to finances, you can set up your own bank account and use your dad's address for documents or sign up for the paperless option (set yourself up a new, private email such as "Dadof 21591@gmail" and change your passwords if you share devices or think she might see your correspondence). If your dad or other family is in any position to help, maybe they could lend you a deposit if necessary? (Although I'm not sure you should be the one to leave the property).
On Mumsnet, people say "get your ducks in a row". Get copies of any financial documents, bank statements, benefits/UC entitlements, salary slips, insurance. If possible, stash the kids' birth certificates and passports somewhere safe, or at least ensure you have digital copies. You can store these on your Google Drive with your new email address. This is a cloud service so she won't find documents stored on a shared laptop, for example.
Check out the terms of your rental agreement or mortgage (and get copies!). Who is named? Is it joint? Do you have a financial liability? Are you able to leave or ask her to leave? Are you able to demonstrate who contributes what?
Keep a diary. Keep note of everything you do for the kids, and also anything that she says or does that causes you emotional or physcial harm. If she behaves in anyway that you find threatening (shouting and not stepping away to give you space, anything physical at all) call 101 and start getting a log of all these incidents.
There is absolutely no reason that you shouldn't get 50/50 custody (or more) and as such, you won't have to pay her anything. You have a financial responsibility to the kids but you're not trying to shirk that so there's no problem. You may have to put the photography on hold (as a hobby? a weekend job?) and get a more reliable 9-5 for a while, but this is only temporary to give you more financial manoeuvrability (spelling?).
Deciding to end a relationship and to leave/ask her to leave doesn't mean that you have to make your move immediately. Get your docs together, write down your reasons for ending the relationship to keep you focussed, find out where you stand financially and if you'd be entiteled to UC/child support with 50/50 custody as a sinle parent, write down your questions and find a free 30 minutes with a solicitor.
You have seen the situation for what it is and you do not have to lose your health, your confidence and your sanity. Start taking steps, even quietly in the background, to arm yourself with information and find a pathway out.