Hello, Daniel is also my great x4 grandfather, through his son William Alfred Eivers.
I too know nothing of him before his marriage. I've never managed to find any online record of his birth in St Croix, or when he came to Liverpool. I've also never found any other people named Eivers in Liverpool who could be siblings/parents.
I found this topic tonight because I've made it my top priority to fill in these blanks. As far as I can see, there is no comprehensive record of immigration between 1804-1825 online, so I'm planning to go to the Record Office here in Liverpool to see what I can find there.
I know of nine children with Mary. In some records I recall Daniel is given the middle name of Dennis. Two of his sons were given middle names - my ancestor William Alfred and his eldest son Lawrence, who appears to have 'Dillon' as his. I thought these are worth noting as they might be Eivers family names.
As for Mary Ann Martinborough, I suspect she was born in Cork, Ireland, as stated on the 1871 census. It's too specific to be an error and I think if she had a West Indies connection it would've been mentioned on one census. I've not made an extensive search for other Martinboroughs in Liverpool yet.