@Dani firstly I am not sure the full extent of your grannies condition. The best I can tell you with limited information is on days where you are having heavy caring responsibilities is to pare back to basics being getting the washing done, floors clean, washing up done and a brief swish and clean of toilets bathrooms if they are dirty on different days. You are fortunate (blessed) there are two carers in the home.
From what I understand you stay at home and husband works ? and baths granny in the evenings. Tag team with your husband more often especially if you are tired and frazzled and find something that granny likes to do to keep her occupied for example crosswords, knitting etc, throwing beanbags/ ping pong balls into a basket (good for co-ordination), inside lawn/ten pin bowls (yes even in a wheelchair with a seat belt so she doesn't fall out) with supervision and light plastic large balls. When you are tired tag your husband so you can do something like go for a walk, have a bubble bath or anything that will let you wind down.
I remember when before DH got diagnosed with Q Fever and he sat under a blanket or slept for literally months and was not capable of anything other than showering and eating that I was exhausted. I lifted him, showered and dressed him, prepared meals, split firewood manually, did rental inspection cleanings on my own etc. I pared back to basics and adopted the opinion if it didn't get done today it would be done sometime in the future and that attitude helped me by not stressing. Then we have had a few depressive incidences with PTSD where DH hasn't uttered a word, sat in the lounge permanently playing playstation and just grunted at me for 4 - 6 week periods. I'd check on him tell him to eat and went out and planted lots of seeds in the gardens and just said when you feel like it pop water on the back deck for me. I found getting away from him but still checking on him helped and the garden is a place I find peaceful or I would go and sew for the while.
Now that DH is getting therapy for his PTSD and depression is getting physiotherapy for his injuries he is a bit more balanced but we still have periods where he is grumpy, demanding and as I am his wife I can say hard to live with. He is in pain most of the time and depending on the day my caring duties will be full peak or very light so I try and keep up with work inside and outside the house with DH's help so that when I have limited time or DH's pain levels are high most things are in some sort of order.
I hope this makes sense and helps you. Bless you for all you do for granny and you will be in our prayers. Talk together with your husband and come up with ideas that will help you both with granny care. Would pureeing the meat help or cutting it into way smaller pieces to cut down the time on meal supervision ?.