Mcdowall of Girvan Scotland

I have a Great, Great, Grandfather James MCDOWALL born 12/7/1827 in Girvan Scotland he married a Jane SIMPSON on the 20/8/1852 in Girvan.
They came to Australia on the ship " Rockhampton " arriving 13/10/1863 in Kepple Bay.They sailed with three children John aged 9,
James aged 7, Helen aged 4 and Alexander aged 2. Helen and Alexander died during the voyage out to Australia.

Jane MCDOWALL nee SIMPSON died in Maryborough QLD 10/02/1864 whilst giving birth to a daughter Jane Simpson MCDOWALL who then went on to pass away on 10/04/1864 also in Maryborough. A Mary MCDOWALL is a signature on this death certificate as sister in law.

James MCDOWALL died in Brisbane 12/02/1865.

I am trying to find out the following.

a. Who was the parents and siblings of James senior
b. How Mary MCDOWALL is related
c. Who cared for John and James Jnr then only 11 and 9 years of age.

James father was John McDowall who married Helen Mooney and they migrated from Ireland between 1800 and 1820.
Children

William B 28/12/1822
Alexander B 28/12/1822
Margaret B 6/3/1825
James B 12/7/1827
Jean B 12/7/1827
John B 18/6/1829
Agnes B 26/10/1832

Does this information assist in my locating details of past or present relatives.

Wayne MCDOWALL