Welcome to Rootschat
I think I can fill in some details for you and clarify some things from this thread.
The Lawrence family of Coleraine are not at all likely to be connected- if they are it would be far earlier than available records. Biffdog (who posted earlier in the thread- see page 2) is related.
The family belonged to Ballylaggan Reformed Presbyterian Church. A few years ago when I transcribed the graveyard there were only 2 (fairly recent) Lawrence headstones.
Starting with the 1887 marriage- David Lawrence was living in Carndugan and the witness William Lorence may have been his brother. The other witness was Susanna's sister Eliza Janie Gray (born 1856). Susanna's parents were James Gray (born c1832) and Rachel Mitchell. There was also a brother James Gray (born c1871).
Susanna (Gray) Lawrence born 25 Aug.1865 & died 20 Oct.1927. David's parents were David Lawrence (son of Samuel) & Mary McMillan (daughter of William).
Children of David Lawrence & Susanna Gray-
1. James Gray Lawrence (1889)
2. Mary McMillan Lawrence (5 Mar.1891)- she died 18 July 1894 Ballylaggan
LINK3. David Lawrence (1893), fought WWI, m.1916 Esther Crawford- 3 sons
4. William "Willie" Lawrence (1895), fought WWI m.1920 Mary Connolly- daughter
5. Thomas Martin Lawrence (1900-1975) m.1923 Sarah Margaret McMaster- 3 sons, 3 daughters
6. Samuel Lawrence (1902-21 Aug.1923)
7. Rachel Mitchell Lawrence (1905) m.1930 John Doey- 1 son
8. George Lawrence (1907) m.1930 Margaret Orr- 2 sons
9. John Mitchell Lawrence (1910)