What do you mean start helping you? Have you not been getting them to help you do things from when they were little?? I started giving my daughter age appropriate jobs when she was 18m such as putting the food down for the cat. She’s 5 now and can load/unload the dishwasher, cut vegetables, tidies her toys away, puts her clothes in laundry basket etc. I would expect an 11 and 12 yo to be doing pretty much everything an adult does including making their own meals, laundry etc. If you’ve not taught them to help from young, you are going to face major issues now they are teens.
Bernstein Bears, Messy Room, Clean House, Chores Are all good books to reference How Mamma Bears handle it
My 12 year old has been doing her own laundry for 3 years and has been unloading the dishwasher and taking out the trash for 2 years. She also takes our 2 dogs outside to potty at least twice a day, makes sure their water bowl is full in the morning and at night, and feeds them twice a day.
Do they have responsibilities of their own? That's a good way to start. My 5 year old is responsible for cleaning up after herself, putting her dishes in the sink, brushing teeth, bathing, changing clothes by herself (I do a quick touch up after), but they just need tasks. It's harder because your children are older and accustomed to how they're living now
Sit them down and have a talk with them and have a talk with yourself about how you plan on reinforcing them to keep it up and be real with yourself that they won’t be perfect at it after a day.