I really felt for you when I saw your OP. In fact I think
"Right. That's it. I have had it with my children. I can do nothing for them anymore. I am exhaustred. I am going to walk out and not come back"
should be in the topic list.
I love mine to bits but sheesh some days I could string them up by the ankles and hang them from the coat hooks.
I find separating them hugely helpful - let one of them do something really messy alone - playdough, paint - sod consequences - and compensate the other with your attention.
I'm not hugely maternal but I've found pretending to be useful - try these
Put them both in a bath full of bubbles and put 5 random items on the side. tell them to close eyes. chuck in 4. get them to find 4 objects under the bubbles and try and remember what the 5th was. repeat.
make big fuzzy felts. Get some rubbish old clothes and cut out big shapes - squares, circles etc and give them a sheet each to make pictures on.
make smell pots. put stinky stuff (orange peel, washing powder tablet, cloves, soap, vinegar on a bit of tissue) in yoghurt pots and put bits of fabric over the top with an elastic band. get them to help you make them. get them to guess whats inside by smelling it.
Teach them to make towers with the flung books.
go on a nature walk - get them to each find a leaf, a stick a stone a feather. Stick them to paper when you get home, give to daddy.
sew buttons to a bit of material - provide wool. Get them to wind wool around buttons to make shapes/pictures
play will it float, will it sink. assemble objects, guess if they will sink in a bowl of water.
Hope you feel better soon. Its exhausting and draining and it spirals down. Summer is coming - life in open spaces is sooooooooooooo much easier....