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I was going to suggest that you check out the 1821 census for Kilmore parish but I think you already located Kellawella on that site. I believe Kellawalla is actually the townland of Killyvally a small (107 acres) townland in Kilmore parish.
Regarding your second question, I would contact the Main Library in Cavan town and ask for their guidance on emigration from Kilmore parish or Co. Cavan in general 200 years ago. You see many instances where one or two families went to a certain area in the States or Canada and wrote back home and invited others from their home parish to make a clean break and take advantage of the opportunites in a New Land.