From what I remember Stellar started as a fork of XRP by Jed McCaleb, who also created XRP. As I understand it, technically it has evolved a lot since then, so I don't know how much of the concept is still shared with Ripple.
As for what this SEC lawsuit would mean to them, your guess is as good as mine. The price of XLM has dropped a little [0] and actually tracks XRP reasonably closely [1].