Each person has 4 rules (pick 2 and use them for the first and middle names).
Note: "related to X" includes X itself.
DW: related to Katherine / something French / ends with "-th" / has to do with water
DH: starts with "Al-" / something Russian / a famous musician / has to do with earth
DD: something Greek / starts with O / a famous athlete / has to do with astronomy
DS: ends with S / something from Shakespeare / something Hebrew / related to Peter
DD: starts with L / character in a book / ends with "-isa" or "-ina" / has to do with fire
DS: a plant or animal / a famous author / 4 or more syllables / starts with "Th-"
DS: a "Mc-" or "Mac-" surname / starts with C / related to John / has to do with the ocean
DD: related to Anna / one syllable / character in a musical / a flower