Death? Dessertion? Prison? John Johnston b Abt.1780, h/o Margaret Johnson (1797) &6 kids flees

Nobody knows what happened to Margaret's husband and why she left Ireland in April 1834 with her six children on a miserable ship ride to Quebec City. We think his name was John. He may have been born in Clontibret and his mother's first name may have been Elizabeth. He is said to have been born from 1783 to 1795. Who knows!  His given name might even have been James but went by John? I can't locate any records of marriages, baptisms, burials for any of them. Margaret was the daughter of George and Harriett JOHNSON. They lived in Armagh Armagh. Harriett (maiden name unknown) died when Margaret was born and George then married a Margaret McCollough in 1799 in Keady. George born in Armagh in 1765 (to Hugh Johnson and Margaret Whitcroft) married Harriett in Armagh in about 1783. We believe Harriett is buried in Armagh but we can't find anything out at all, anyway, Margaret, their daughter married John (or James) Johnston probably about 1817. They had: Margaret (1819), Samuel (1821), James Mystery of what happened to John or James JOHNSTON b. Abt. 1785, h/o Margaret Johnson (1797) (1823), John Johnston (1824) (my Great x2 Grandpa), William (1825) and Maria (1829). They all left Ireland in 1834 except John.  It' odd to me that from the children's records of birthplaces this family moved constantly! From Armagh to CAVAN to Clontibret Monaghan to Clones. Then back and forth. Doesn't look like short distances between them either. Was Dad on-the-lamb for some reason? Did he suffer mental problems and have to be hospitalized? His constant uprooting his family was squirrelly for sure! But, I think he died between 1829 when Maria was born and 1834 when Margaret left Ireland.  It's interesting that Margaret had arranged to have John baptized by the Church of Ireland in Clones for April 1832 but it wasn't John who got baptized there that day! James was instead. Where was Dad? Some say he died 1n1852 still in Ireland. Some say he got remarried? It's all such a big mystery! For years I've tried to find out about him but nothing works. Help!