Since husband will not help, hire it.
Consider a house keeper once a week to clean the kitchen, (clean out fridge every 2 weeks) bathrooms and laundry. Or see if your mom can also do some of this. Pay her for her work. If she will not take the money, put it aside and do something special with her or for her later on.
Hire a college student to pick up your children from school, get them home, make snack and help with their homework.. and then start your dinner. This way your mom can leave when she needs to, (look into a elderly transportation for her.,) it gives you a little more time to get home.
Do NOT make calls while driving.. ever! You are already overwhelmed and you do not need another distraction while you are driving, and we other drivers do not need a distracted driver on the road. Use this car time to listen to calming music or a book on CD so that this can be a quiet time of your day.
Or ask your mom if she can make the appts, based on your needs. Your mom can also at least prep for dinner.
Make a weekly menu, keep lots of staples in your pantry. Consider doubling everything you make so you can freeze half of it for 2 weeks later. Keep freezer bags and a sharpie in the kitchen so they can be labeled.
Many doctors etc, you can now make appts online, check and see if that will work. Ask them to email communications to you Can your mom take the kids to their appts? My mom has always taken my sisters kids to all sorts of appts.
I am concerned about the amount of courses you are going to attempt to take and keep up with.. Even a full time student with no other obligations would have to really keep up with their studies, reports, etc.. to stay on top of as much school work as you are about to take on..
You will be sacrificing time with your children, you can teach them to be big helpers by, helping to keep the house clean. Taking their dirty clothes straight to the laundry room, putting their clean clothes away, they can learn to fold their own clothes, change their beds..
Start eating on paper plates. Teach your children how to make salads. How to put the dishes in the dishwasher after they have rinsed them.
Playdates only on weekends at your house. If they are invited to others during the week, see if the college student can drive them and pick them up, before agreeing.
Get as much rest as possible and do not neglect your health or this fragile house of cards is going to all fall. Your children need a happy and healthy mom. I am sending you strength.