Oh I feel for you op!
First of all big massive hugs to you. The worst thing ever when you feel you're just treading water
Try sitting everyone down . No distractions so no TV no phones etc.
Tell everyone how it's impacting you and be brutally honest. I always say it's the smallest things the make a huge difference such as scraping food off your plate and popping it in the sink to soak before washing, putting lids back on toothpaste, put your laundry in a basket, if you walk past a packet on the floor, pick it up and bin it etc etc.
The older ones could do some bigger chores such as one puts a wash load on and the other tales it out and hangs it to dry? Work together and halve the workload BUT it's one massive thing that YOU don't have to do. It allows you that breathing space to focus on YOU be it a hot cuppa or watching some shit tv for 30 mins.
My sons are (almost) 10 and 7 and I tell them repeatedly that of I can't get to their rooms they don't get hoovered/cleaned/bed made etc. Then if they get spiders that's not my problem because I haven't been able to get shit done.
I recently joined a gym and go swimming 4 to 5 times a week because i was sick of all the housework and getting nowhere (seemingly) - is that an option for you? Get out of the house and tell everyone that they pitch in?
Get a huge whiteboard and let them pick what they would prefer to do - washing, pots, mopping, dusting, clothes putting away, stripping beds, hanging clothes to dry etc
Sorry for the essay but I feel that I could have written this x