Step Children Maintenance

Just wondered whether anyone had any advice on step children and spouse maintanence.
I am married for 9 years and I want to seperate.
I have decided enough is enough and we cannot live under the same roof any longer.
I FEEL LIKE A PRISONER WITH NO ESCAPE
Their biological father has never paid anything.
Will I have to pay maintenenance?
Please help if you can?
The house is paid for and Im happy to leave that as a one of lump sum final payment.

Childrens ages 13 & 15 They have little or no respect for me I try to advise their wrong doings and any telling off they run to the support of the wife or inlaws so there is no parental control on my part.

I am in full time employment 25k
Wife full time work now 16k

I pay all the bills my wifepays for clothes school trips and activities but no money goes into the bill pot. Her parents have supported the children ever since they were born clothes , education trips family holidays etc.

Ive been emotionally blackmailed every time I have threatened to leave about making sure that I get screwed for every penny.

I have rarely had my input in the childrens welfare care and upbringing without any influence from inlaws.

They always insisted loaning us money when we want to take a loan out say for new boiler and so on so Im paying them back on the never never they also make sure the kids never do without even if I think its the wrong decision which is often.

any advice what I can do even how to start the ball rolling would be helpful

You won't have to leave her all the equity in the house,and a judge wouldn't let you either.Too unfair on your part.
the woman with kids normally gets more like 70% / 80% of the house equity.That's the real
money grabbing ones who really want to squeeze every last drop and make you pay like your wife is stating.
The kids even though not yours biologically could well be viewed as children of the marriage after 9 years so you might get collared for child maintenance of 20% of your take home salary.She won't get spousal maintenance by the time she gets all the single mother handouts on top of her £16k she'll have a bigger monthly income than you.
If you have any sense you'll knock her for that each month if the real father can't pay for the kids don't think she'd pursue you.
Don't let the money worry you if you're getting no respect all the way round leave em to it.
All the best
Pete