This is part of doing your tree.
My grandads da, wasn't the father of the rest of the kids in his family, the other kids dad died 7years before he was born, and his dad was the lodger, who, changed his name to the families to save confusion. they never married, well not that I can find yet.
My other nan, the great uncle I thought was my great uncle, wasn't. He was raised by my great grandmother as her own, and he always thought she was his mom, until he found out his mom, was actually my great aunty. she got pregnant while her husband was away at sea, and he told her to get rid of him on the train track, but great grandma took him in as her own.
My other grandad, left home at 13, lied and got in the army, when his mom died, his dad married her sister, who he had already fathered a child by before his wife died.
So be prepared to find things like that, I just find it intriguing.
Love the poem too.