Having a brainstorm,
noticed your gt gt gt grandfather was a Robert. So wondered if maybe he was named after wife Mary's, father.
I found another Mary Okell on IGI, born in Gt Budworth, where you mentioned they married. One slight difference is her age being born in 1778, that makes her 29 (nearer to Joe's age) her father was a Robert, no mother mentioned unfortunately. Perhaps worth another look see, you never know.
This doesn't help with the 2 Joe problem, sadly.
Jean