Step grandchildren - AIBU

Low carb food isn't difficult, my DH does this to keep type 2 diabetes at bay. ( He was diagnosed about 2-3 years ago but has successfully reversed the condition) . Just cook your usual meals but don't serve potatoes or pasta,rice, bread etc.
Get the children to help you, give them tasks to do, get everyone out for a walk, to the park or whatever is near you.
If the son wants washing done point him towards the machine.
I understand that you were a single parent , but some people need a bit of support and a nudge in the right direction.

It's that bit harder for you as it's your DH's DS, but wildswan is right, your house, your rules.

My DS was a single parent for several years and found it hard to stay on top of everything. But he did cope with the washing, cooking etc. although discipline was a bit lax because he had to manage the best he could.

Don't try to cure everything at once. Pick just 3 or 4 things that irritate you most and see what you can do to change them - ask stepson to put washing in machine, girls to lay table as suggested. Mention to stepson that it helps if you know dietary requirements in advance - even make a point of asking him next time.

He probably hasn't even realised....

Your house, your rules. Yours son can eat what you put in front of him, or go out and buy his own. The girls likewise.

Tell the girls calmly, to please turn down the volume - and could one of them please set the table and the other one dry the dishes. Tell your lazy son to put the laundry in the washing machine and remind him that although he is your son he is a guest in your house and he and his girls have to respect your home.

Alcohol is probably going to do little to help the situation.