I checked the microfilm copy of 1st Boardmills Church held by PRONI (Public Records Office)for the children of John and Sarah.Unfortunately Sarahs maiden name is not legible so cannot confirm maiden name.I agree James was married to Sarah Tamihill The Carrick could be an abbreviation ,the Downshires were major landowners in County Down and it is possible they were the Maxwells' landlords. There were 3 Maxwell families in Boardmills at same date John Maxwell/Sarah ?  (my family?) James Maxwell/Sarah Tamihill (your family?) Hugh Maxwell/Margaret Clark The assumption would be they were brothers As you have found it is difficult to research ancestors in Ireland Will keep you updated if I find more Best Regards Rod