Hi Donald I'm in Adelaide and do free research for anyone requiring information about ancestors who came to South Australia. I had a look when I was in the library a week or two ago for information re your William & Ida Lawson.I see you already have quite a bit of information about them, but I hope the little I have to contribute may be of some help to you.
ARRIVAL FROM OVERSEAS.
William Ramage Lawson and wife (unnamed) arrived in South Australia 30th September 1864 aboard the "Countess of Fife".
Our marriage records go from 1842-1937 in S.Aus. I have searched them, but there are no marriage records for any of the three children.
I also found the following on the International Genealogical Index:-
William Ramage Lawson married 23rd May 1864 at Kirriemuir, Angus, Scotland to Ida Eisenhuth