It's difficult to advise without more information but I can imagine you don't want to share too much.
Firstly though I really think you need to get advice from a specialist domestic abuse organisation - there must be one in your country? Or you could contact the UK national domestic abuse helpline.
It's not very clear from your posts exactly what your husband has agreed to in terms of you moving to the UK with the children. Has he agreed to a temporary move, or a move until further notice, and is that on the understanding that you return to the country you're in now at some point? You say you need to hide the fact that you want to separate, so does that mean he thinks you will take the kids to the UK while he stays where he and you are now, but you remain in a relationship??
I think that you are in a tricky situation regarding the legalities of it, and if you do take your kids to the UK with the intention of staying, you should get legal advice first, and if possible get your husband's agreement in writing.
There are some good UK-based organisations with informative websites and helplines too - they are Rights of Women and Child Law Advice. I'll dig out the links. You should probably try and find advice based on your country of residence too.
Lastly, you say that your 1-bed flat is currently rented out. I'm sure you're aware that you'll need to legally evict the tenants before you can move in. Have you evicted tenants before? Do you know how the process works legally and how long it takes?
Do you have any family or friends in the UK that you and the children could stay with temporarily until you can sort a suitable place to live?
You will eventually become eligible for benefits and housing help in the UK once you are 'habitually resident' but you'll need practical and emotional support in the meantime.
There are a lot of aspects to consider but you can take it one step at a time. If you do just one thing please reach out to the national domestic abuse helpline or your local equivalent.