Hi Liz,
My grandfather, many generations back was the brother of your Mary Featherstonhaugh. His name was William Featherstonhaugh, born 16/03/1774. I have Mary and William's father as Marmaduke Featherstonhaugh, born 1739 and he lived in Hermitage House, Chester-le-Street.
I have Thomas and Isabella Featherstonhaugh's father in my family tree, he was Marmaduke Featherstonhaugh, born in Chester-le-Street, 1577 and died in Chester-le-Street, 1632.
I have approx 100 Featherstonhaugh connections in my family tree, feel free to send me a PM if you require additional info on them.
Regards, Alison