Hello and a warm welcome from me too. Taken from the non-conformist registers arethe baptisms for the children of Simeon Harker ( occupation - miner) and his wife Betty at the Low Row Indpependent Chapel in Swaledale, Yorkshire (sorry no idea where Swaledale is, but hopefully someone else may!) which may be of use to you.
William Harker 5 October 1797
Mary Harker 7 July 1800
Sarah Harker 2 July 1804
Alice Harker 22 Jan 1807
Simeon Harker 12 August 1809
For the baptism of Simeon (jnr) & Elizabeth residence is given for parents as Heights Near Gunnerside, Swaledale
Elizabeth Harker 4 May 1811
James Harker 12 December 1812
Simon Harker 12 December 1812
James is 3 years old and Simon 3 Weeks when baptised and the parents abode is given as Brownsey, Swaledale, Yorks
Whilst I appreciate there is no reference to Thomas as a son of Simeon, I noticed that the name is spelt as you have said Thomas's son's name was spelt - Simeon, so maybe a place to start looking. Given the dates - maybe Simeon was an uncle ?