It is possible that the parents were still alive for the 1841 census, but the problem is with the name William Turner. There are so many of them in Staffordshire.

It may be that their father was also a locksmith, which may help narrow it down a bit.

Presumably you have collected all the information related to their convict lives, musters, pardons etc? I think that convict Indents sometimes give information about family members in the "remarks" column (I have seen this on Tasmanian Indents but unsure about NSW).
If you post a section of the writing including the difficult to decipher mother's name, we can offer our opinions as to what it might be.
Have you looked for Turner/Reilly marriage in Staffordshire?
