Henry Mathers and Elizabeth Brown are also my Gt-Gt-Gt Grandparents and I am descended through their son Robert Henry. I guess that makes us 4th cousins.
I have found Robert Henry and Elizabeth Brown rather hard to track down. It was only when I decided that since Elizabeth arrived at about age 2, she was likely the daughter of a convict so maybe she also married one, that I started to make a bit of progress. I still have quite a lot to follow up (she may be mentioned in the Colonial Secretaries Papers for example, but that will be a big job for one day when I have time). I only have that her father was Robert Brown and her mother was ?Kelly. She was born at West Meath in 1822, Ireland, and they were married at St James in Sydney when she was about 14 years old. I know the dates might be all over the place.
My brother found an internet site listing Robert Henry as having been courtmartialled in Gibralter for robbing an officer, and transported to NSW colony, I think for 7 years. But I have not seen the website myself yet.
I have more of Henry and Elizabeths 'tree', but would love some info about the later generations. I know that Jane had 7 children, and I know of 5 of the next generation.
Does any of this fit with anything you know or are interested in? Do you have any further information about Henry or Elizabeth?