A: Definitely use both-- it means you'll have twice as much brewing strength for your first batch! Moving forward, with every batch you brew, a new culture will grow on top. You can keep brewing with numerous cultures, or just one, and use the new cultures to start additional brews, share with friends, etc. We recommend keeping no more than 3 to 4 cultures in your brew at a time. Simply toss out the oldest, darkest brown cultures as you go along.
To explain what's happening, the darker brown one is the "older one" and the creamier one is the "newer one." At some point during their growing period at the brewery, the original culture had some kind of a disruption during its growing that caused it to grow, then drop to the bottom, then it regrew an entirely new culture. It likely fused partly together, which is how they got packaged together.