Bit of a blood bath this one!
I’ll bite op.
Don’t forget that if you only have them 50% of the time some of your outgoings will drop slightly. So food for 5 people may cost you £60 -£80 per week, but food for just you for the week may only end up being £20 for the week, same goes for things like your gas and electric, when the kids are at their dads you will probably find the cost of this goes down slightly, if your on a water meter again this should in theory drop slightly. Showers/baths for 5 people will be significantly more than you having a shower during the week. You need to take a proper look at your finances and get a grip on what you can cut back on.
If the kids do clubs etc arrange for him to pay for when he has the kids and you pay for the days when the kids are at yours (again drops your expenses slightly). If you don’t already arrange for him to pay half for school uniform, so he pays for the shoes and school bags, you buy the trousers and tops etc.
If you haven’t worked for 13/14 years it WILL be hard getting back into the work force so you will probably end up with something very much entry level, but the longer you leave it the harder it will be. If the oldest is 13 then your ex won’t be liable to pay you anything for them in 5 years so your money will drop whatever you do. You can’t expect him to keep on paying for your lifestyle.
If you can’t afford to loose 250 per month then don’t buy your kids an Xbox to score points against your ex, and throwing out comments like you can keep them 100% because I don’t get money for them is an awful thing to say, all those kids will understand is that they are some form of financial transaction. I think if you work less than 16 hrs a week your benefits wouldn’t be affected. You could look for something like waitressing work on zero contracts and say you’d be available to work any hours week 1, but week 2 you can only work school times. It’s not ideal but could help you in the long run. If your ex lost his job tomorrow you would get fuck all.
You comment about the kids going for 2 weeks away from their dad is daft, most kids would do 1 week at yours then 1 week at their dads.