Please help me find John Stewart's lineage info born Belfast 1833

We have got to finding John Stewart Born 1 September, 1833 Donaghadee/Castlereagh, Belfast. Whose father was John Stewart (farmer)and mother Isabel McDowell.

John Stewart Junior married Mary Peden 31st March, 1856 Newry Arm, Ireland. Mourne PArish. Newry Civil licensed by W.Henry.

They lived at 136 High Street, Newry. He was a confectioner, worked for James Grant where he did his apprenticeship for in Belfast in late 1840's-1856. 

We have exhausted all the Heritage websites and  Census records, and we just cant find any further relatives up the braches.

Our main aim is to find all the Stewarts we can. John Stewart jnr had 3 children called Matilda (born ireland), Hugh Joseph (born Australia, and Isabel (also Born Australia).

They migrated to Australia in Nov 1856.

We figure they had to have migrated from Scotland at some stage. but our lineage seemed to have settled in the Newry areas.

Would you be able to direct me as to whom or what I should do in order to following these leads.

We are coming over in September, and would like to at least find John Stewart senior place of birth and his parents aswell.