The wife of the John Montgomery who emigrated to US in 1923 was named Charlotte so it seems the one in the 1901 census is not correct. The family had been living in Edinburgh prior to travelling to US and the oldest child on the passenger list was Charlotte aged 9 yrs 9 mths on 1 Nov 1923. Wonder if the parents married in Scotland and may have been living there for some time - may be another reason why not found in Irish census.
Suggest looking for family in Scotland census (I don't have access to it) and trying to get marriage cert in Scotland Edinburgh perhaps as this should show both parents names.
annclare