I have done a bit more digging and established that both Eliza and Morris were granted authorisations to marry in Liverpool synagogues in 1890 (Old Synagogue) and 1892 (Princes Road Synagogue) respectively, which suggests that their parents were in possession of their own ketubah. Maybe the simple explanation is that Joseph and Mary had married in Poland before emigrating.
There are a couple of family trees on ancestry reporting (without any evidence) that both Joseph and Mary came from Lomza. I really can't make out Mary's birthplace as it was recorded in 1871 census. It appears to begin with a "W". Do you have other records that show their places of birth?