Realize this is an old post, but if you're still searching or anyone else is, I have a bit of oral history that fits in with what you already know. I'm descended from John & Isabella's daughter Emma, who was my grandfather's grandmother. According to my grandfather's notes:


"John Ackroyd lived in London near St. Paul’s Cathedral. He told about hearing the cathedral bells in his home. He graduated from Oxford University. Left England to avoid service In the British army and changed his name to Johnson (a name just plucked out of the air). In Philadelphia he worked in the City Hall.


He married a daughter of Scottish immigrants named Moffett.


John Ackroyd Johnson and his wife became parents of ten children. The eldest of these was Emma Johnson born in 1841. John and his wife died within weeks of each other leaving Emma to raise her nine brothers and sisters."