I would delete both logs, but also send a follow up email right after you do it.
Explain to the first person (multi) that signing their name on the log is required and also maybe point out that there is more than one stage. Be nice and informative about it.
For the second I would just say, "I noticed you logged xxx twice, probably due to a glitch in your smartphone logging. I am deleting one of the logs. Thanks for finding my cache.
Here you can read more about log deletion: http://support.Groundspeak.com/index.php?pg=kb.page&id=204
I've deleted "extra" smartphone logs on I think 3 occasions, and one of them logged 4 or 5 founds. I pretty much sent polite emails along the lines of what I'm quoting, although I deleted the logs first. None of these finders ever wrote back. Who knows, there's a good chance they never even look at the website on a computer, and don't see or care about their statistics.
I sent emails to both cachers in question. The duplicate logger acknowledged a possible smartphone error, and thanked me for informing her. The phantom finder has not responded to a polite request to change his log to a DNF. I tried to be as nice as possible, but it's hard to say "I'm deleting your log" without sounding like a jerk.
