I wish I had a great deal more knowledge and a great deal more certainty over what we know or believe. First of all Radcliffe of Ballaradcliffe is, as you will be aware an Andreas family, and remained thus into recent times.
The family I have been looking at is Radcliffe of Knockaloe Moar, which is just south of Peel and is where the WW1 Alien Internment camp was. The male Radcliffe line became extinct in 1789, but his second wife was the sister of a girl I am descended from. However if we go back another century or so, a Knockaloe Daughter married Deemster Thomas Norris, who I am descended from, so I can trace my roots back to Knockaloe Moar.
It is possible, indeed quite likely that the two Radcliffe families were related, but you may have to go back to the 1500s for that to happen, and I do not have a definite answer to that. I haven't researched it as I do not have any known links to Ballaradcliffe so far.
Unfortunately the Radcliffes collectively are probably the subject of more gibberish than almost any other Manx family, and that is saying something. An account of Ballaradcliffe was published in the 1930s, and can be praised for its entertainment value and as a work of fiction, but as a useful research tool, it needs the same kind of warning that the government demands are put on cigarette packets.
Ironically, there was one useful pointer in it that I overlooked because it is so unreliable.
Going on to the Knockaloe family, two very reputed researchers, Rita Browne and J A Brew both say that the founder of the Knockaloe line was a Thomas Radcliffe who was the last Abbot of Rushen and was the younger brother to the 1st Earl of Sussex, who was in turn the 10th Baron FitzWalter, and therefore son of the 9th baron who was beheaded in 1496.
First of all, Thomas Radcliffe was NOT the last Abbot of Rushen. His identity is known and it was NOT Radcliffe. Frances has raised an interesting query. "The Friary" at Ballabeg is on the site of the old and very small Bemaccan Friary, and when it was dissolved by Henry VIII, it went to the Tyldesley family as a house. The Tyldesleys and Radcliffes of Ordsall Lancs had some connections, so Frances has asked "What is Thomas Radcliffe was the last Abbot at the Friary, rather than at Rushen. It was small, obscure and largely forgotten, so it could work out, BUT THAT IS SURMISE AT PRESENT.
Apart from Thomas Radcliffe definitely NOT being the last Abbot of Rushen, there is the possible link with the Barons FitzWalter. The Fitzwalter tree in ENgland from the 1st Baron to the 9th Baron is straightforward, and the title was forfeited for a decade as a result of treason. The evidence relating to the execution of Sir William Stanley at this time was highly dubious, and the same applied in my view to the evidence leading to the execution of the 9th Baron FitzWalter. The principal witness was a fellow conspirator who had been unmasked and then used to spy on other people, and the more heads that rolled, the more firmly his head would stay on his shoulders ! Ten years later the title was restored to the 9th Baron's son, who was later created 1st Earl of Sussex. The Fitzwalters were an Essex family for generations. All this UK genealogy is perfectly straightforward and I have no problems with it.
Where it starts to go pear shaped is that Rita Browne and J A Brew both say that Robert Radcliffe, 10th Baron FitzWalter & 1st Earl of Sussex had a younger brother, Thomas, who became last Abbot of Rushen. In what I would call authoritative accounts of the FitzWalters there is no firm evidence for a younger brother, though several rather questionable accounts do include one, but they seem to work on the basis that there needs to be one if the story is to fit, so there must have been one. Thomas Radcliffe MIGHT or MIGHT NOT have been the younger brother of the Earl of Sussex, but he assuredly was not Abbot of Rushen.
Who was he then ? That is where it is a nightmare. In the early 1500s, a Thurstan Tyldesley, who almost certainly is the same guy who held important posts under the Stanleys in the IOM in 1532, was executor for a deceased member of the Radcliffe family of Ordsall in Lancs. The Stanley Earls of Derby were not from the big railway junction in the Midlands, but from West Derby Liverpool, so were a Lancs & Cheshire family. When they became Lords of Mann they brought in families they knew to run their new kingdom, and that included the Tyldesleys, Prestons, and other Lancs families such as the Radcliffes.
In my opinion, it is far more likely that the first Radcliffe to hold Knockaloe was a Lancashire Radcliffe rather than a FitzWalter Radcliffe. There is a legend, I believe handed down in the Christian family that one of the Milntown daughters married an Abbot. Now there have not been any Abbots on the Island since the dissolution of the monasteries, and before the reformation celibacy was the rule, so that suggests that if a Christian girl did marry an Abbot, it was an Abbot who had lost his job.
IF, and this is a massive IF, Thomas Radcliffe was the Abbot of the Bemaccan Friary, then he would have lost his job in 1536 so would be free to marry. "Marry an ex-abbot" would then be true, but over the next five hundred years, the specific abbey could get lost with the obvious assumption that it was the obvious one of Rushen Abbey.
The idea that Frances put up of Bemaccan is fascinating and well worth exploring, but we cannot say, "it is so".
That is where we are, with a Thomas Radcliffe who came from England some time before 1539, and MIGHT have been an abbot but not of Rushen. He was probably from one of the Lancs Radcliffe families, altho Rita Browne and J A Brew claim he was a FitzWalter Radcliffe. I can't prove he was NOT a FitzWalter, but proving a positive connection 500 years ago is hard enough, and to prove a negative connection is very unlikely.
So, there it is. There is a splendid book by Sally McCambridge on Andreas which may help you with Ballaradcliffe.