You're likely correct about Catherine. The only extra info in burial register is that CC lived at Balnahowe Rushen
William Watersons
ch 29 AUG 1819 s/o John W/Mgt Maddrell
ch 09 OCT 1819 s/o Henry W/Ann W
ch 28 MAY 1820 s.i Henry W/Jane (Harrison)

Catherine Waterson Quark did have brothers named Henry and John. Wm 43 in 1861 is probably a relative maybe even a nephew.
WAAAAY too many Wat(t)ersons!

Of course you're probably right about the name being Turnbull--some of the misspellings nab me sometimes.
DJD