I have checked James Orchard Halliwell's "Dictionary of Archaic and Provincial words" (London, 1847) and all the obscure words in Bronte's line seem to be genuine dialect, but they don't seem to make sense.
"Bairnies" is presumably a derivation of bairn, still commonly used for baby in the north of England.
"Grat" means wept,and is from Northumberland.
"Mither" means muffled, and is from Northamptonshire.
"Mools" means rumple or disorder and is also from Northamptonshire.
So the line reads something like "It was far in the night and the babies wept. The smother beneath the rumple heard that..." .

I think Bronte probably made it up, and it still sounds like Rambling Sid to me.

If you do a Google search on "yorkshire dialect" there are a number of links to relevant societies and academic sites which it may be worth contacting if you want to look into the linguistic provenance further.