I totally understand and sympathise with you as we have very similar circumstances. All my family is abroad too. A schedule might be worth considering. Your 7 and 5 yr olds should be able to do some work independently. Have you heard of "Managers of Their Homes?" This has helped me order our day and feel a sense of accomplishment daily with our 3 children. Dd 4 enjoys workbooks and sticker books, painting, and gluing so this frees me a little while I teach her brother who is 6. Meanwhile DD 2 gets an old, used workbook for "school". She insists on doing what her siblings are doing otherwise it gets chaotic. When I have one-on-one time with DD4, DS 6 plays with DD2. These are just some of the ideas I glean from MOTH. Also, we are done with school by lunch time except for reading to the children and DS fun reading time, which we do for an hour after lunch/break.
I also feel a need to spend time alone (which is why I am up at midnight-bad habit though!)otherwise I get weary and irritable. When DH comes home, he helps by giving baths to the children.They are amazingly calm around him. Meanwhile I get out my audiobook on the ipod while cooking and doing chores and that's quite satisfying to me. After dinner DH makes me escape to the bedroom and lock the door on some days for about half an hour to recharge. I have also found grocery trips alone bring a measure of serenity. I had to find new ways to recoup my energy. A nice long brisk walk is something I really look forward to but it doesn't happen consistently. Wish you the best!