I have three good explanations. First is if you look in the Somerset Archives. Type in George Turner Seymour Tyntesfield. One hit talks about deeds done in August 1840, when the estate was already called Tyntesfield.
Two, I have a poem here written in 1839, when the mother Marianne Seymour and two of her siblings left to live in France, and there are two references to Tyntesfield in a poem of 1839. Thirdly, my Great Great Grandfather, Arthur Penrose Seymour, bought a farm in Marlborough, New Zealand, which he named Tyntesfield (after the place he was born, and grew up in).
There is no doubt more out there to prove this, but I am convinced it is airtight!
By the way, I also believe that William Turner of Belmont is Louisa Cam's Uncle, not a paternal Uncle of George Turner Seymour as some books attest.
Thank you very much, keep up the good work! I look forward to hearing more about Belmont, were there any paintings done of this house that are old?
Many thanks for the pictures also.