Edward Selwood was my Great, Great Grandfather (Married Edward McTaggart's daughter, Mary).
I've never found a record of them returning to Scotland - but I also wasn't aware of Ellen's second husband?
I have found a useful tool for the Gympie Cemetery where you can search for positions of graves online. I found Edward & Mary's son, Thomas' grave, I went to have a look for Edward & Ellen (Helen's), but its not letting me in right now, please have a look:http://www.gympiecemeterytrust.com.au/index.php/research/dec...
Another good place to have a look at the details of this line is on sellwood.info, it was put together by Viv Sellwood and traces through the families complete with stories and photos (there are none of Edward & Ellen, but a couple of Mary McTaggart. Feel free to also look at my tree as I have some more photos.
I have traced Patrick back to Ireland, there were a few Prodestant McTaggarts in Ayrshire that originally hailed from Islay, but also a family that came across from Cork, in Ireland, this time a Catholic family. I definitely found a Patrick McTaggart from Maybole that fits this description, and had a son called Edward, and a Granddaughter named Mary. However,I have not yet been able to find a definite connection to say they are the same person. Feel free to drop me a line.