There is this entry on the 1891 census in Port Glasgow that might connect:
James McKenzie 33 publican's assistant, b. Lochbroom R&C
Agnes McKenzie 28 b. Ladybarn (?), Renfrewshire
George McKenzie 1 b. Ladybarn, Renfrewshire...maybe connected to the 1890 birth notice?
Margaret McKenzie 2 b. Ladybarn, Renfrewshire
Helen McKenzie 64, mother, b. Lochbroom R&C
Address: No 3 Laird Street, Port Glasgow
These are only just possibilities, cranstone. Hard to add more without you checking some of the details to see how they may fit with what you are looking for...
Monica