Searching for Parents of Henry William Schulz Dob 14 1 1880 IN Prussia

Plenty data about him but no data on US Declaration or other US forms. Not sure if city of birth Luiden - maybe Luidenhoffen. Father died between 1880 and 1898. Mother remarried and probably died before 1898. No known siblings. Father and mother did not emigrate to US....HOW DO I FIND THEIR NAMES??