Do go and ask about depression.
I see you have a plan about bathing. That is great. And look at you -- you have a diary and you use it!! You are well on your way.
You are a brave woman to come on here and ask for advice, and have handled it with grace.
Wrt cooking: my mum used to have a (really boring I thought) routine that involved a roast dinner on Sunday - chicken or beef, followed on Monday by leftover roast with more potatoes and veg, and sometimes followed on Tuesday by some sort of hash chopped up bits of beef/chicken, spuds chopped after being boiled a bit, and onions all in a pan. If nothing was left for Tuesday we had something else that day often spag bol, with leftover spag bol on baked potatoes for Wednesday. Then on Thursdays and Fridays we sometimes had macaroni cheese, sometimes fish fingers, sometimes spaghetti with meatballs. Saturday was often a fry up for dinner - rashers, scones, sausages, maybe some salad.
She varied the weekday offerings with the odd curry or shepherd's pie (or actually cottage pie, made with mince.) We also had the occasional fish pie, steak and kidney pie (sometimes leftover roast beef and peas and carrots pie) and chicken pot pie (again with leftover chicken and some frozen veg). It was all simple meals, and leftovers repackaged. Sometimes we had soup on Saturdays, with scones or brown bread. Sometimes it was lamb's liver with onions, and potatoes and green veg.
For lunches we had lots of scrambled eggs on toast, beans on toast, lots of bananas and other fruit, and yogurt and toasted cheese. School lunch was always cheese sandwiches with fruit and a sweet snack.
When I first started out preparing meals for the family I tried elaborate and very varied meals and ended up in a heap and with a fridge full of leftovers I would eventually have to throw out. So back to simple routine I went. I turned into my mother. My DCs are fussy eaters and simple turned out to be best. However I never serve kidneys and can't find lamb's liver where I am (I actually like it sliced really thin).
I have since then branched into using the slow cooker and batch cooking. I mostly use the slow cooker for soups and chilis and curries. I make split pea soup and minestrone mostly, and freeze soup bowl sized portions. For chili I do the meat and spices and sauce but add beans when I heat it up to serve. I keep a large amount of browned mince in the freezer and it's handy for many recipes. It goes in the slow cooker for chili, or I use cubed lean pork that just goes straight in. Curry (chicken) just all goes in raw. I use a variety of starches -- couscous (cooks really fast), rice, pasta as well as potatoes, and every so often we have a pizza.
We eat tonnes of toast here -- my old toaster packed it in a week before Christmas and I replaced it that very day. We were completely lost for several hours without it.
Frozen veg can be your best friend -- green beans, onions, sliced peppers, diced carrots, even garlic, make meal prep quicker. Pesto is great for a quick topping on pasta, with parmesan. Frozen pastry and phyllo are great too for packaging leftovers.
I don't do dessert every night. On weekends if I had time when the DCs were small we used to have something simple like jelly or a little ice cream, or apple crumble if I was feeling really on top of things. Or cake from a box mix. Frequently we had a packet of biscuits.
See what you can do with simple cooking. You can look up roasting times per pound online. Get yourself a meat thermometer.
I think it's fantastic that you like to socialise and have a good group going, and you can keep it up in moderate amounts as well as keeping everything ticking at home, as long as you don't get too ambitious and try to do too much. Start with easy cooking (roasting is really easy) and if a routine with bathing seems to work then stick to that.
I think you are going to have to make the rellies a little less comfortable in your home -- ask them to make their own cuppa and raid the biscuit tin while you get your own thing done if you find it hard to put your foot down and tell them straight out that they are arriving at a really inconvenient time for you. They may lose interest when they lose their captive audience. Or just keep front of house lights off or don't answer the door. If they phone to say they are on the doorstep tell them you are bathing the kiddies, sorry, bad time...