Thanks for sending in your sources for Syrena McDaniels. It would mean checking the orginal sourcework of the people who submitted the info to LDS/IGI (familysearch.org) to know if the info was reliable. I don't know if you have used the LDS site extensively, but you have to use caution with it. These were sometimes very well researched but LDS did not require proof from the people making submittals and many errors are now distributed as fact because of that. I have seen some real doozies from IGI - like people dying in the US but recorded as buried in England a few years earlier!! LDS material is a good starting point, but you then have to go to original sources (like vital records, deeds, probate, etc.) to make sure what is in the LDS record is true.
Since Nelson McDaniels was a resident of Maine, a call or trip to the Maine State Archives might be a great place to start. They are responsive by email as well and seem willing to look things up for you. They would start with their VR files, especially if you have a death date for Nelson that is after 1892. I limit my research to the Harriman family. I don't think Nelson and the Syrena McDaniels that married John Harriman are siblings.