Have cracked the puzzle of Denis/Dennis McColl. He was actually Daniel Denis McColl,but known as Denis to tell him apart from HIS father Daniel. Daniel Denis McColl was born 13th Dec 1850,Dumbarton to Daniel and Elisabeth McColl(nee Muir).
Other children were Elizabeth McColl born 18th June 1847 and Paul McColl born 7th April 1853,both Dumbarton.
Daniel McColl married Elisabeth Muir 11th April 1846 Port Glasgow.
Elisabeth Muir was born 17th October 1829 Paisley,Renfrew to John and Janet Muir(nee Cameron). John Muir born about 1791 Kilmaurs,Ayr. Janet Cameron born about 1795 Kilmaurs,Ayr.
Daniel Denis McColl married Margaret Gibson 17th July 1868.
Margaret Gibson was born 22nd Dec 1856 Coylton,Ayr,to Andrew and Margaret Gibson(nee Brown). Andrew Gibson married Margaret Brown 8th March 1853 Langholm,Dumfries.
This is as far as I have been able to trace,in just 1 day,after coming back to the puzzle(after several months) with a fresh mind !