I'm Dr. Jackie, a mental health therapist, professor, and relationship expert. I am so sorry to read what you are going through. Perhaps you can provide some more information so that I can help you better. I don't see a specific question except you do not know what to do. I'm not sure if you are asking for advice about abortion;adoption;keeping the baby--all kind of options? Or advice on how to tell your family? So if you can be specific about what you are asking, I can give a better, more informed answer.
It sounds like you have your hands full with 3 children already. I am hoping you are getting some type of assistance or help so that you can be a good mom to these children. Plus, you need to take care of yourself. If you want to keep the baby, then you should be able to contact your county agency on family--Children and Youth. Many people do not want CYS or CPS involved, with good reason. So if you do not want them involved and want their assistance, Planned Parenthood or other non-profit organizations in your area should be able to provide information on WIC and other services that can help you while pregnant and caring for your other young children.
I know you are scared. Again, you do not mention if your family has been supportive to you through the other 3 pregnancies. If they have been supportive before, yes, they might initially be upset but because they are worried about one person caring for 4 young children. You don't mention if the father(s) is/are around. If they are, this is even better. If not, do you have friends, other family members who can help? The more support you have, the better you and your kid will be. But that is why I suggested some of the other agencies--they are there to help you so that you can focus on what is the most important--your beautiful family!
Let me know if this helps, please. I can send you the information from JA if you want to chat on the phone or Skype if that will help more.