Genealogical Uncertainty

I shouldn't even post this about my pathetic genealogical troubles, but since I almost had to write it out anyway to help clarify my mind, here it is. I realize very few will have any interest whatsoever, but I know that some of you do have some experience and may have thoughts.

I have recently posted that I can trace Scottish ancestry back quite a way, and I have more recently unearthed some Cornish ancestry which also goes back quite a way. However, I have had trouble getting past my GG Grandfather, William Robinson. This is the Irish side of my genealogy or at least one of the Irish lines.

We know that my great grandfather was Israel Robinson, and it seems certain that his father was William. It was there that I drew a blank on the Ancestry website. Perhaps I require a higher level of membership, but I decided to try familysearch.com of the Latter Day Saints denomination (Reorganized Church of?). 

Here's what I think I know for sure about the this branch of the family from the Ancestry site. 

• According to the 1851 census, my G Grandfather, Israel, was 14 and was living with a William Robinson, age 66. The census lists William as bring born in Ireland, and it follows that would have been ~1785.
• There was also a Mary Robinson, age 51, who was born in Canada. Presumably and later confirmed, this would be William's wife and Israel's mother..
• The next census, 1861, shows William as 74 (not 76?) and Israel as 24. It doesn't list a wife named Mary although she, apparently from later data, lived until 1881.
• I also have a record of marriage between, Israel Robinson, and Elizabeth Drew on December 31 1872. William Robinson and Mary Brown were listed as parents. Therefore, I am as certain as can be that William is my GG Grandfather and that he was born in Ireland ~1785. 
• I think that I can also be sure Mary Brown was William's wife and the mother of my grandfather, Israel.

That was as far as I could get on the Ancestry site, so I scuttled over to FamilySearch and began to input data. It became both interesting and confusing.

• There was a William Robinson born in Ireland ~1785, and he married a Margaret McDonald (perhaps McDonough) in Ireland. They had three children from 1811 to 1819.
• Although it would seem that he could have been any William Robinson, FamilySearch records do have this William Robinson as also being a person who died in Stormont, Ontario, Canada in 1876. This fits my GG Grandfather just about perfectly..
• If this was, indeed, my William Robinson, his parents were James Robinson and Mary Mead (back on the Irish side of the ocean again).

Questions ensue.

Is this really the same William Robinson, and, if so, how come the multiple wives? (It also looks as though there was even another wife before his Irish wife, Margaret McDonald.)

Keep in mind that his Canadian children don't appear on the scene until 1827, with my Great Grandfather Israel not being born until 1836. William, the randy old goat, would have be siring children in his forties and even into his late fifties as he kept reproducing even after Israel. Therefore, it is possible that he could have had children with Margaret in Ireland from 1811 to 1819 when he would have been in his late twenties and early thirties and then with Mary Brown in Canada 8 years later.

Could William have had two wives, one in Ireland and one in Canada? Indications are that if so, his Irish wife would have still been alive when he was in Canada, which is puzzling.

It's an interesting little mystery that will, quite possibly, remain a mystery.