Wow - quite a bit of information to absorb and piece together from what I have. I believe the Miller you found is indeed Meller/Mellor as my records show Meller and Mellor. Here is the lineup that I have from Ewan Christian to me:
Ewan Christian
Edward Christian
John Christian
Edmond Christian
Matthias Christian
John Christian m Catherine Callow (?dau Wm. Callow)
John Christian m Catherine Oates
Robert Oates Christian m. Jane Sayle
Thomas Phillip Christian m. Julia Longford Meller/or
John Longford Mellor Christian m. Christian Faith Kelly
John Longford Lee Crellin Christian m. Carro Jennie Beatrice Ensign
George Longford Mellor Christian m. Genevieve Podulka (dau. Elaine Maria Christian Semanik)

I believe I have the will of Robert Oates Christian of Washington Terrace found during my visit to IOM in 2000. It bequeaths to dau Jane Sayle Christian Crellin all goods, etc., incl Washington Terrace, and the proceeds of the sale of The Flat, Ramsey, the latter of which appears to have/had been entrusted to? William and Thomas Corlette. Dated 7 Sept 1866.

While on IOM in 2000 we visited the property I believe to be Washington Terrace aka Washington Mount, although it looked like a new or rebuilt construction.

I have a letter from Kneale & Co., 12 Oct 1937 to my grandfather John Longford Lee Crellin Christian notifying him of his cousin Caroline Jane Lucy Christian entering into a contract to sell Washington Mount for the sum of £1700.

Another letter, 9 Nov 1937 contains excerpts from the will (of which I have a copy) of Jane Sayle Christian Crellin (d. 17 June 1927) bequething Washington Mount to her daughter Caroline Jane Lucy Christian, and upon her (CJLC) death to John Longford Mellor, her cousin or his heirs if he is dead by then. That's where my grandfather John Longford Lee Crellin Christian comes in as he was the first-born living son/heir of John Longford Mellor Christian.

The Washington Mount property is just "down the road from" the stone building containing adjoined cottages: The Nook and Cooil Roi, Ballure Road. The sale of all three are detailed in a Real Estate Account: £2,705.17.11

As this is a lot of information, and I am interested in how Jayne Sayle Christian Crellin and Caroline Jane Lucy Christian are related - as "cousins", I will post a separate inquiry.