Recently, my family took turns getting sick. My mother-in-law said that because there were many symbols posted on the door, who could help me see what these symbols were for?

First of all, I can be sure that your door is opposite to his. These symbols posted by their family belong to Wang's own family, and all the shaqi is brought to your family, which is prone to illness. For example, sticking a small round mirror on your door can drive Shaqi to their home, which is not good for their home. The symbols they put up are like small mirrors, which are not good for your family.

I suggest you secretly tear it up for him, or find a feng shui gentleman to show it to your family and come up with countermeasures to fight back.