Stress is what allowed our cave person ancestors to be able to react to a charging mammoth. Your body is trying to store up energy for the coming emergency. Our bodies aren't really equipped to handle emergencies like financing a new company or dealing with regulations or interviewing employees.
Scheduling anything when you have little ones is very difficult. If you can get away for a few hours a week, you might consider looking into other exercise classes. It might be a good way to network with other people who are in the same boat as you. It also might be a good thing to network with massage therapists. (A good part of this networking could involve you lying on a table, listening to gentle music, while someone releases the tension in your muscles.)
Another idea that might be win-win for you is to try out some workout DVDs. They might give you some ideas for your classes. Our local library has over 100 to chose from. You can do these at home, so it will either be easier or harder, depending on the kids.....
You may feel like you are being self-indulgent trying to take care of yourself when there is so much to be done for the business and your little girls. But you are not. You are worth it. And if you can do something to remove some of the stress in your life and take a little time for yourself, you will be better at everything else.
"There's treasure everywhere." Hobbes, in Calvin and Hobbes