Hello werriwee, Thank you for your post. It is exciting to make contact with a descendent of Eliza Lynch and William Crabb! I am a descedent of Eliza's brother Daniel and have been tracing this branch of the family for many years. The wife of another descendent of Eliza's brother Daniel has also done some excellent research on Eliza and William's story which she shared with me. I am aware of Marcus's sad end, thanks to the great resource - the Australian Trove.
When Daniel Lynch (born c. 1823) emigrated from Cork to Sydney in 1850 aboard the Cornwall, he indicated that he had a sister Margaret and a brother Marcus in Moreton's Bay. I learned of this record many years ago but it was only a few years ago that I learned Eliza had emigrated with her sister Margaret, brother-in-law Michael Sheehan, and the two young Sheehan sons circa 1841. Margaret and Michael were married in the parish of St. Mary Whitechapel in London in 1838 and their first two sons were born in England before the family had two sons before emigrating to Australia. Other siblings for Daniel, Marcus, Margaret, and Eliza included John Lynch, Ellen Lynch,and one additional son, name unknown. John Lynch (christened 1 April 1824) is still a bit of a brick wall but it is possible that he may have died young or gone to the USA. Ellen moved to London and married the artist Henry Parsons Riviere in St. Pancras in 1849. Presumably Jeremiah Lynch was deceased prior to 1850 when Daniel emigrated from Cork as he named his next of kin as his mother, Mary (Anne) Lucey Lynch and gave her residence as London. In 1851, the widowed Mary Lynch she was living with Ellen and Henry at 36 Charlotte Square in London, and she died at the home of Ellen and Henry in 1859. Henry and Ellen separated sometime between 1861 and 1886. Ellen moved to Dublin and lived at 4 Pembroke Road near the Elgin intersection until her death on 26 Feb, 1906. Her niece, Lucy (possibly her brother John's daughter?) lived with her for a period in Dublin. Margaret Lynch Sheehan died 12 Ot 1891 in Albury, NSW. Daniel died 7 Apr 1890 in Sydney. And, I expect that you already know that, Eliza Lynch Crabb died 11 Nov. 1873 in Queensland.
This sketches in a little of the family history. I do know quite a bit more, am happy to share, and would love to learn more about Eliza's descendents, including you.
Thanks for posting!