Welcome to the forums and thanks for reaching out. It sounds like you have a lot on your plate at the moment and you are finding it hard to work on yourself and find your 'me time'.
It's great that you are trying to improve yourself and pursuing your career goals, I can imagine it wasn't easy to make that decision. It takes a lot of hard work and determination to work and study, as well as look after a family. This isn't easy, but through your hard work, you will attain a degree and hopefully find a better job and grow in your career.
It sounds like you have a lot of responsibilities with the kids and the chores around the house, does anyone help you with them by any chance? If that is not the case, maybe talk to your partner about a way that would be suitable for both of you and the kids to contribute around the house as that might help take the load of you.
In terms of your work environment, I understand that you are doing this on a casual basis, have you looked into finding another job? You might find work less stressful if you are working in a better environment. If that is not an option for you, hopefully you will find a better job once you graduate.
I know COVID has prevented everyone from enjoying life and going on a holiday, but now with no lockdowns, we can live somewhat a normal life. Have you found the time to catch up with family and friends? I think if you reach out to them you might find comfort in talking to someone. If you don't feel comfortable talking to them, then I would suggest to talk to a professional to help you through this tough time. You can speak to your GP for a referral to see a psychologist or counsellor if you are interested. There is a free online chat service on Beyond Blue and phone service on 1300 22 4636 available.
It sounds like you need some time for yourself, if you can, try to schedule in some alone time everyday and discuss it with the family. Whether it is going for a walk or exercising or even winding down in your room and reading a book. I know you don't have a lot of spare time, but by having an hour or a few minutes to yourself each day, this can help you recharge and accomplish more.
Hope this helps.