Hi Col,
Do you have details on the births of these people? Particularly have you any information on the parents from a Baptismal registry or similar?
John is a new name as a child of Sarah’s but as she would have been about 25 in 1810 it is quite possible.
I have a Family Search doc for a Charles Lynchey born in 1816 in Ireland.
James could not have been born later than 1828 otherwise he would have been too old to accompany his mother to Australia, unless the James you refer to died and a further son was named James.
Peter
Melbourne
Australia