on paper he might seem like the parent that is able to provide more. In reality he is a emotionally abusive thug who has no problem subjecting the people in his family that he is supposed to protect to battery and torture and if he has no problems vocally abusing you in front of the kids then he will have no problem doing it to them when he feels that they are no longer falling into line.
Hitler on paper was a wonderful son, highly motivated, great job, well dressed and smart looking.. but off paper the man was also a fucking pysco headcase.
You have listed all of your concerns and reasons for not wanting to take the children with you. Even though you have heard many first hand accounts of women who have been through the same system and told you what will happen with regards to housing, benefits, child maintenance, tax credits and emotional support, help with furnishing, moving costs, help with parenting courses ect but you are unwilling to take any of this on board.
You are able to do this if you want to.
If you leave your children with this man or his parents he will systematically to to turn the children against you and destroy any hope of you having a relationship with them in the future.
Having less money or fewer friends or relatives does not make you a shit mother.
Abandoning your children and leaving them to live with a abusive monster does.
Because regardless of how scary the future seems to you, how you worry about coping you have to put the children's safety first.
If you have the ability to hold down a part time job. Run a house. Live with abuse and conduct a affair all at the same time i am sure you can mange to google and find out your options instead of giving up before you have even started.