How do you mommas feed your twins? Are they just breast fed or formula fed or both?

I have twin boys who just hit the 2 month old mark. I originally wanted to just breast feed them but my supply just isn’t enough. So I breast feed when I can, pump, and supplement with formula.

Also how do I increase my supply? I’m getting about four ounces when I pump every two hours. Which would hardly feed one of my boys now that they are drinking 4 ounces or more each feeding.

Thanks