First off, I am sorry your father is so ill. I wish you and your family well as you go through this difficult and emotional time.
I have not had to hire an assistant but I think it is a great idea. Why not put an ad in your local paper for a flexible mature person with proven experience with young children in a professional setting. I would also explain to your clients the situation and how you are adjusting your business so that you can accommodate your family obligations and your business obligations.
Good luck.