Here is card #4 (card #3 is the most challenging; I will try to read it later).
As a friendly reminder in the New Year of 1917. Taken up in the hospital.
Stamped: Reservespital Leipzig / __-Krankenpflege (this was a hospital or other type of medical facility). Given the year, I would say that perhaps he had been wounded during WWI.
Addressed to: Mrs. / Rachel Lederfried [note that her last name is written differently here than it was on the first card) / Gross Holletilz / Post Miechelob
Brooklyn, New York, USA