Carolyn & Ellen,
F.Y.I.;
I recently discovered that Issachar appears to have been born during 1854.
Per St. Cath's Index an "Issachar Trugen" birth was registered during the June Quarter, 1854 in the Bodmin Registration District, Cornwall. Luxulyan is located about 12km/7.5miles south of Bodmin, so in consideration of repeat Census references to Issachar being b. in Luxulyan, it is reasonable to assume that Luxulyan was located within the Bodmin Registration District.
In due course we must check the Passenger List for the "Earl Derby" - inwards shipping to Brisbane on 20 June, 1879 after 3 months at sea, departed London 15 March, 1879 - per Brisbane Courier, 21 June, 1879.
Regards,
Clarke.