I have traced the ancestry of Daniel McDonald Senior.
He was born illegitimate to Mary McDonald who was the widow of James O'Hara. His biological father I later found was John Richard Roger. Mary had three children with him in 1889, 1893 and 1898 but never married him. She then married Thomas Lochhead in 1899 and had two more children.
Also, Fofarian, were you assuming there was meant to be any logic behind the name change? If there's one thing I've learned from my grandpa's family is there is no rhyme or reason to anything