I return with a proposal: could Greer's dad be Audra's cousin (through Audra's mother, who has no existing backstory whatsoever?) That could still make the Greengrasses the closest British connection to take them in, and doesn't involve any retconning of Audra's background. And Victorian families were playing pretty fast and loose with the "cousin" label anyway so that still gets us to 'cousin Greer and cousin Lorelei.'

Olive also said she's open to retconning but this seemed like a pretty clean route so wanted to see what you thought! @"Daffodil Potts"

So just for abundant clarity: Edith Crouch nee [--] would be the sister of Patrick Owen's mother or father, Audra and Patrick would be cousins, Greer and Lorelei would be second-cousins to Ford and co.