All Threlfalls, Trelfalls, Treffalls, Threfoes, Threlfords, and similar seem to have a common origin in a comparatively small area of Lancashire, and so, ultimately, to be related, so that should be helpful in tracing back - but as in early records in that small area no-one seems to have said WHO they married, and to have shared use of a very few, very common first names, there's a real cat's cradle in the mists of time that no-one without a time machine will be able to sort out finally.
"Meanings" of the name presented over the years include being from a clearing where thralls (serfs?slaves?) had settled, either as freed from subjugation or merely by hopping it, to various terms connected with harvesting(??), fording an unidentified stream (The Threl? - no, I think not). My money is on the scarpering serfs!
And as as far as I know there was only one big Threlfall who was "sirred" officially, in the Preston area, and thus likely to have obtained a Coat of Arms, I delight in the complex variations I've seen hanging on trees over the years, that'd probably give the College of Heralds apoplexy!
Perhaps as an escaped serf that's why I'm quite pleased never to have found any real Nobility Connections?