Hi Ian,
Nice to hear from you. I remember your family quite well, because some time ago I was helping the Clan MacLennan with their worldwide tree and I worked on the John Urquhart / Margaret MacLennan families. It wasn't easy because there were 2 couples with the same names in Gairloch more or less at the same time.
Our 9 children for John and Margaret match, but I have one extra child: Catherine, born 25 Dec 1809 in Gairloch (but she could be daughter of the other couple). Do you know if your child Alexander became a boatbuilder? If yes, then Catherine is his (and your Elizabeth's) sister.
As for Margaret MacLennan, I have her as daughter of Finlay MacLennan and Elizabeth Ross. There are no records for this couple, but I have these siblings for Margaret:
John, who died 2 Apr 1859 in Tignafilin. Apparently he married Isabella MacKenzie.
Kenneth, born c1773, died 29 Mar 1864 in Aultgrishin. He married Flora MacRae 16 Dec 1806 in Melvaig.
Isabella, born c1785, died 15 Apr 1860 in Melvaig (record gives mother as Mackenzie, but this is possibly a mistake). She married Duncan Urquhart 8 Jan 1808 in Melvaig.
Janet. I have her as daughter of Finlay MacLennan from Melvaig, marrying Donald Bain 24 Feb 1818. The couple had at least 3 children: Mary (15 Dec 1818), Murdoch (6 Sep 1826), Catherine (19 Jan 1830).
It would be great to know more or less when Elizabeth was transported to Tasmania. I guess she never returned to Scotland? If this is so, it would help me sort out which child Alexander belongs to which John/Margaret couple. Both couples had a child Alexander, born quite close one to the other, one died in 1889 and the other in 1895. The informant of one of those deaths was an Elizabeth MacKenzie, sister, so that would be the other family if your Elizabeth never returned to Scotland.
Cheers,
Francisco