Do I need to submit visa app in person?

Do I physically have to submit it in person? I’m reading that I dont have to but it says I must sign it in person. I’m confused as to how that works. Also, my husband and 2 children are going to Beijing too and I need to know if I can submit the applications for them or is there a service that can do this for all of us. We live very far from New York and paying a visa servicing company would be ideal if possible.