heaross,
You say Mary Ellen Johnston ( nee Burns) was born in Tynemouth.
Did you mean actually born in the town of Tynemouth. Or that her birth was registered at/with the Registration District (RD) of Tynemouth ( main office in the town of Tynemouth)
I can see on FreeBMD the registration of the birth of a Mary Eleanor Burns in June Quarter of 1874 at/with the Registration District (RD) of Tynemouth. As the Tynemouth RD covered a wide area which included several other towns and communities, this birth could have been in several locations.
A candidate for Mary was the dtr of Patrick and Ann, born in Walker, a part of the parish of Longbenton, which lay within the jurisdiction of Tynemouth RD. Today Walker is part of the City of Newcastle.
I notice that FreeBMD site records Robert's surame as JOHNSON, in the registration of his marriage at/with Gateshead RD ( which like Tynemouth RD, covered a wide area around Gateshead, e.g. Heworth, Felling)
Michael Dixon
Newcastle