Looking for Johnston Family Originally from Ireland

Hi

I am looking for the Johnston family whom were originally from Ireland, unfortunately i do not know where in Ireland though. I have got a Robert Johnston born abt 1860 in Ireland he married a lady called Sarah (maiden name unknown)also born in Ireland abt 1867. Robert & Sarah had 4x children Margaret born 1889 in Ireland, Sarah A born 1892 in Liverpool, William P born 1897 in Liverpool & Martha born in 1899 in Liverpool. Looking at the dates the family moved to Liverpool between 1889-1892.

William P Johnston married Maud E Grainger in Gloucester 1918. Maud was born in Gloucester 12th March 1896 & died in Gloucester 1976. I believe William P died in Gloucester 1959.

If anyone has any information that would be of help to me it would be great to hear from you.

Many thanks