Looks as if MJW has found the info. for you
this is all I was able to find I'm afraid from
http://www.sl.nsw.gov.au/research_guides/convicts/instructions/con_trans_reg_dbase_trial.htmlWilliam Shannon, one of 290 convicts transported on the Exmouth, 03 March 1831.
Convicted at Lancaster Quarter Session for a term of 14 years.
Vessel: Exmouth.
Date of Departure: 03 March 1831
Place of Arrival: New South Wales
John Shannon, one of 169 convicts transported on the Mellish, 10 November 1828.
Convicted at Lancaster, Liverpool Boro' Quarter Sessions for a term of 7 years on 28 July 1828
Vessel: Mellish
Date of Departure: 10 November 1828
Place of Arrival: New South Wales
If you require details perhaps MJW will be able to provide the crime for John that lead to his transportation - looks as if his info. can be found on A.....y but unfortunatley I don't have access
There was also a trial in Lancashire Jul 1827 for a John Shannon but he was acquitted (don't know if this would be the same one)