Okay, the thing I wanted to say about your brother is that the scenario where you look after your mother in Spain instead of her going into a care home is not a viable one. Presuming you separate, you would lose primary residency of the children and you would have to pay your partner maintenance from what ever you earned in your business and job. There is also no guarantee that your partner would send the children over and you would unlikely be able to afford to go to court to get an order. On the other hand, the situation would benefit your brother as you would be there looking after your mum.
So you say that you asked your brother for lawyer’s details? Did he give you them? In other words, do you have the name of a lawyer recommended?
Did your brother offer any practical ideas and support for getting your own flat etc in the U.K.?
Because if not, it sounds a bit like he is another man who is going to give you his opinions and then leave you feeling like you are falling short. It really is not helpful to berate victims of abuse for failing to leave without offering concrete support and help for them to do so. If your brother has offered you concrete, viable help and support in the U.K., follow up on it. If not, then okay, his words simply more bluntly tell you what you already know. But they do so in a way which suggests you are failing, when you are not. The reason controlling men use the tactics they do is because they work.
But the good news is that you are beginning to see that and you said yourself before the conversation with your brother than things need to change. You are going to be able to manage this but you will need nerves of steel. It is a case of feel the anxiety and plough on through regardless.
So with my previous list of priorities, do you and your brother have a plan for your mum? Even as simple as - can she manage to September/October and you both come out again?
Do you have space to get on with your job amidst all this? If you go back to the U.K., you are going to have to remind your partner this is your only source of income and that you cannot be doing all the domestic stuff 24/7. He is still going to have to take the children to buy school uniform etc. You simply will not be available as you need to work. He has told you how important money is, so that should be clear to him.
Children - I think if he won’t agree to send them to Spain, then the only choice is to make sure that you have flights booked for all of you in autumn (I mean, you and the children, because your partner will be looking for a job and taking his well-earned break from domestic duties (sarcasm) and given that he has put obstacles in your way previously, there is no reason he gets to come). Ask your brother to pay for the flights if you need to. Be prepared to go to court and ask for an order to take them if your partner refuses. There is no court which would not allow you to take your children to see your deteriorating mother overseas. (A good way to cut through the emotional manipulation is to think in terms of what the law allows you to do).
It is very, very important not to take on the burden of guilt and apologetic persona that he is trying to force you to. There is absolutely nothing unreasonable in staying in Spain an extra couple of weeks to care for and make plans for your mother, given her illness. He is the other responsible parent, looking after the children is his job too. You need to be very, very clear in your own head about this and prepared to push back on any suggestion you have been unreasonable. (I do think, however, there is a point that the longer you stay, the more you risk losing your position as primary carer in legal terms, should you separate any time soon; however, it does not seem to me that separation is on his agenda, even if it may be on yours. Nonetheless, it might help to think about the situation in legal terms to guide what you do, as the law is not emotional).
I think it is very, very important to have a plan. Think about your plan as an anchor. It is going to hold you firm in a storm (and he will whip up a storm). Know what you want to achieve. If and when you go back to the U.K., you are not going to be his whipping boy, you are going back to achieve things on your plan.
I remember my lawyer saying to me very early on I needed to develop a thicker skin. She was right, but it is not that easy. I preferred to think of it as I needed to put on my tin hat (as in the World War One type, not the tin foil ones) and plough on through, regardless of what came at me.