Hi Annie,
Yes it certainly sounds like there was some confusion going on at the time of the death. These things did happen a lot, with a son either giving his own name or his fathers name at the wrong time. If they were rather illiterate, a lot of these errors were not noticed. I think if you accept that this is his arrival in 1840 with Samuel then he is Samuel's son. The other thought of course is he was Thomas's son, not Samuels and therefore he arrived at another time and this is not his immigration record.
I have actually been sitting here fooling about with this looking for other possibilities. By what I can see from here, if he is not Samuel's son then the immigration does not appear to be online, so may have been later and you would need go to library to check passenger lists for other possibilities. Hate to have to mention it but there actually is a widowed Thomas aged 51 who weds in Burra in 1850 so anything is possible. (Long way from Adelaide, where Thomas wed but should be mentioned) There is also the death of a Thomas in 1868 aged 34 in North Adelaide. Rel William Terrell probable rel) So there was certainly more than one Thomas about.
I will say I cannot find a Sarah Angove in the marriage index and it really should be there if the name is correct. When you look at Trengove/ Angove you don't think of them as much alike but when you start saying them, they really do sound similar. I notice the naming patterns with Samuel and Thomas's children are similar.
Unfortunately if these children were all born before Sep 1/4 1837 then I am afraid all you will get is the mothers Christian name on baptism entry. SA marriages do list a couple of possibilities for the other sons born pre 1840. (No Guarantees of course)
TERRELL Samuel 22 Single father Saml =
LINNEMANN Johanna Christiana Emilie 22 Single Father Christien Linnemann 10 Feb 1857 Trinity Church [Adelaide]
Dist Ade 29/94
TERRELL John 30 Status Not Recorded Father Saml =
LANE Mary Ann 17 Status not Recorded Father Thomas Lane 17 Jul 1866 Trinity Church [Adelaide] Dist Ade Symbol V 68/137
It looks like there were a few Terrells around St Uny by the burials. Including a Samuel and a Thomas Henry
http://ourworld.compuserve.com/homepages/jon_rees/steunyT.htmI would suggest you try an email to the OPC for St Uny and hope she can help. The baptisms will at least list an occupation for the father.
http://www.cornwall-opc.org/PAR/Q-S/Redruth.htmDoesn't rain but it pours.........Good Luck..........Kris