Hello @sean12341
I guess what you are trying to achieve is:
Once you have resized a container to 6 column, you are trying to divide it again by 12. Such that the components inside it would resized by diving the resized container by 12.
That would not be possible. However, you can modify the default number of columns for the root container to greater than 12 and then adjust grid.less accordingly.
Thus, the UI would be divided into more number of columns, allowing authors to resize components more precisely.
This article covers Responsive Grid in detail
https://blog.developer.adobe.com/customizing-the-aem-grid-3ff9c2121a36
Aanchal Sikka