I’m looking at the options of the weight paint brush, and I don’t see the X mirror option. How do I paint on both sides now? Any help is appreciated. 
I tried that but it didn’t work. 
The symmetry x doesn’t work because I don’t want the bone on one side to influence the other.
I found a youtube video that answers the question, but I guess mine still didn’t work, does the mesh have to be completely symmetrical for the Mirror Vertex Groups to work in weight paint?
Here is the video by the way: https://youtu.be/oI_TX5qblSQ
Yes, it does
What if the topology is symmetrical but the shape itself is not completely symmetrical, will it work or not?
That will work, it just needs the same topology. AFAIK, anyway, you’ll have to try it
Is there a way to fill everything with blue weight paint all at once on all bones? Without having to select or painting each individual bones or vertices.
Ctrl P to Armature > With Empty Groups
After I made empty group with armature, using the weight paint brushes don’t seem to work properly. When I am using the Smear brush, it is painting red and when I use the Draw brush and set weight to 0, it still paints red. Here is the issue: https://drive.google.com/file/d/1K22jkY7J7W2Js59oA0b0B0xpquDbKjqG/view?usp=sharing