My sister-in-law is descended from a Tyack line from Sithney, Cornwall: James Tyack (Abt 1811 - 1873) and Elizabeth Clarke Lobb (Abt 1814 - 1866).I have their marriage certificate that shows them as being of full age and James is a Bachelor on 4 Dec 1851.So I think that James father Richard (b abt 1791 Sithney d bef 1851) married a Mary or Mary Ann.It's confusing because there appears to be two James Tyacks born around 1811.
As far as I can show James and Elizabeth Lobb had three children: James (Abt 1852 - Abt 1880), John Lobb (Abt 1854 - Abt 1878) and Richard (b Abt 1857 Mawgan - d 21 Aug 1940, Maxstoke, Warwickshire). My sister-in-law has this Richard's school book in which he adds an "e" to his surname to become Tyacke. My sister-in-law is a great grand-daughter of this Richard and she lives in Warwickshire.
Some of this detail is on my web site www.antill.org.uk