Its not easy to get vegetation under pine trees.

If you look at the forest floor in a pine forest, there's not much growing there... competition for light and water and pH are all factors.

I'd look for plants that can tolerate dry shade you should be able to have some success. And of course there is always the option to add supplemental water for the plants that you do plant there.

Grass isn't going to be the best choice. You may want to try hostas, ferns, wild geraniums, jacob's ladder, bishop's cap, meadowrue, ginger, columbine. Its quite common to see a nice landscaped, mulched bed of shade loving plants under pine trees.