I found a messy fix to correct the font size and line spacing issue I was having by adding <p> and </p> within the short code:
[one_half] <p> text </p> [/one_half]
It is far from ideal so if anyone knows a better fix, I would appreciate it.
To add spacing betwen the two colums when they become stacked (smaller screen), I added padding in the css file:
.one_half {
width: 48%;
padding-bottom: 20px;
Thanks