Paul, I wonder if this is our William's first marriage?
Ireland Diocesan and Prerogative Marriage Licence Bonds indexes 1623-1866 Transcription
First name(s) William
Last name Mulholland
Year 1840
Diocese Armagh
Spouse's first name(s) Isabella
Spouse's last name Dalzell
Category Birth, Marriage, Death & Parish Records
Subcategory Parish Marriages
Given that, in Scotland, the surname Dalzell is pronounced Dee-ell, I wonder if over time and said with an Irish accent Isabelle's surname has mutated to Dale.
These are all possible children of our William and this list was compiled before I knew about you ancestor.
Eliza, b ? Married 1873, f. William, m. Not named
Isaac b. 1847, f. William m. Not named
Joseph b. Abt 1851 f. William, m. Isabella Dale
Jane b. Abt.1858 f. William, m. Not named
John b. 1861 f. William, m. Mary Quin
Samuel, b. 1862 f. William, m. Mary Quin
John Mulholland and his wife had more children than you have listed. Two sons named William, two named John, Joseph, James, Mary Jane, Sarah, Annie and Elizabeth - not necessarily in that order.
William Mulholland and Janet Geddes had several children not just Sarah Martin Mulholland.
Samuel Mulholland and Agnes Jeanie Dunlop had quite a few children.
As far as I am aware Samuel Mulholland and Eliza Hadden Wright had no children. He died in 1915.