My thoughts on this...

Rough that there were fatalities, but as far as your career prospects go, the NTSB placed the blame on the magneto. You would not be the first professional pilot whose history involved in a fatal accident, nor the last.

The facts that you had flight following, communicated the emergency, and turned toward land prevented your actions from being contributory to the ditching...you did everything you could.

If the pax had not got out of the airplane then the failure to brief the ditching could have been named a contributory factor, but since they all got out that's not really relevant. For a low-time private pilot, you didn't do too badly.

If an an airline interviewer wanted to be a real @sshole, he might ask why you flew an ASEL out of power-off glide range from land and why you didn't have life vests. These are not regulatory requirements, and while they might reflect on your judgement I would suspect that low flight experience, not bad judgement, was the issue here.

I think you are fine career-wise...anybody who sees this will recognize it for what it is: A learning experience with the ultimate negative reinforcement.