I remember you said you found Women’s Aid unhelpful.
The way I was referred was through
www.scottishwomensrightscentre.org.uk/
Rights of Women will also be able to advise you legally in broad terms, although you need a solicitor. The Family Law (Scotland) Act 2006 does make some provision for cohabiting couples, although less than if you were married. However, because you are not married, hallelujah, you do not need to reach agreement on the child arrangements before you can get divorced (can you imagine trying to do that with a controlling person??? A whole other nightmare. Mind you, the Scottish government are looking at the law around cohabitation and I really hope they do not decide to include that part for everyone’s sakes. But that is my bugbear and luckily does not affect you). Once I was referred, I found WA helpful. You need to say that you recognise your relationship is characterised by coercive control and that he has been violent in the past (putting you out of the car is physical violence) and that you are afraid of him. It is a hurdle to get over to see yourself in this position, but that is the truth. No shame attached to being in this position. Either Rights of Women or WA can refer you to a contact in the Citizen’s Advice Bureau who can advise financially, including if you are eligible for legal aid.
Returning on the 7th takes you to 21 August. Caring for a vulnerable and sick relative would count as essential travel. So you can go. Does your travel insurance cover you? Or are the European health card still valid? Arguably taking the children is also essential so they have a chance to see your mum. If your mum is in the Canaries or Balearic (sp?) islands, they are not subject to quarantine.
www.gov.uk/foreign-travel-advice/spain
I think you said you can work on your job and business over there so you are in a fortunate position to be able to travel and still work. (I do not think you would be unreasonable to take the children, given the circumstances).
The problem is as someone said upthread, he has trained you well and you probably also have the experience like I did, that he is relentless in his arguments and makes everything unreasonable on his part seem reasonable so you doubt yourself.
You need to decide if this is an argument you want to pursue with him or if you want to focus your attention on getting out of this relationship so you can do what you want. If you want to put your foot down and say that you are going, and taking the children with you (make sure you have the passports in your possession), he will not get an emergency child welfare hearing before you are due to travel. However, you do need his consent to take the children out the country, so you need to ask him outright if he forbids it.
As we were in a legal process and then a court process, I always travel with a letter of permission from ex. The first time I was so stressed about asking, but he has not ever refused to give me it. If you don’t have the same surname as your children, you might get asked at passport control (we get asked every time by the same lady, it is a bit of a running joke now).