Ayrshire to Victoria Australia

Seeking information about the siblings of my great-great-grandfather John MITCHELL who may have come to Australia:

RobertMITCHELL b.1820
James MITCHELL b. 1823 (definately came to Aus)
Thomas MITCHELL b. 1830
William MITCHELL b. 1835
Jean MITCHELL b. 1838

James MITCHELL was in Durham Lead, Victoria in 1861.

John MITCHELL came to Australia in about 1852 with his wife Janet PURVES. They lived in Durham Lead near Ballarat and owned the Black Bull Hotel in DL.