I think Elizth was Manx born (her dates fit perfectly + she + bro are missing from 1841 census and of the 'right' parish to emigrate to Ohio) - I suspect however that John + Elizth may have travelled on different ships - possibly marriage was arranged before her arrival ?

John Clague is still the mystery - have you found any other record of his age other than the 1800 birth quoted on MI - did American marr records of that period name parents?