I can't believe I'm reading this. op seems to have not a clue. I appreciate that these children are her sc, but really? 
You avoid them and you never discipline them but you claim that their father is a good father?
No, he's clearly not because he doesn't seem to have done barely any parenting over the last 10 years either!!
"demanding dinner and not contributing in anyway, I.e. helping wash up" and having a sulk over Wanting a Fryup and been told that no you can't have a Fryup because tonight's dinner is chicken and veg.
So where was the dad in all of this ? why didn't he turn around and say don't speak to op like that?
These children haven't been parented at all, they've had no guidelines, no discipline, no structure, no nothing.
because if they had had all of those basics they wouldn't speak to you like that in the first place.
I've got two teenagers at the moment and quite frankly I agree with previous posters they're not the most attractive right now!!
I find them very irritating, self-centred. but I have done proper parenting in the last 15 years so I expect respect, help : they have chores to do. Ds1 has to clean the bathroom, DS2 has to clean the downstairs toilet and pair the socks etc.
they come to the table, when called, eat what they are given, they say thank you after every meal I've prepared for them. they show respect as they should do.
I find teenagers these days and peoples parenting style for teenagers quite horrific to be honest!!
and everyone just says all that's the way they are. No, I think they're allowed to be more self-centred these days than certainly I was allowed to be as a teenager.
I think parenting has changed for the worst.
however this doesn't help the OP's problem.
you really need to start with some of the basics. and you really need to talk to your husband about it. and he should be doing a lot more and talking to them about how they treat you generally.