I'm not a native speaker but I'll try my best:
written from the barracks in Pötzsch, Saarbrücken on 4 March 1917
on the back you will see your son Carl. Warmest regards and kisses and see you soon (good bye). Greetings and kisses also for Trudy and Tita.
Dear Mum, Trudy and Tita,
from our way to the barracks I'm sending greetings from my heart. On the back you will see my picture. We are staying here for a day and had a picture taken. I will tell you my address later. Warmest regards and see you soon. Carl (can't read the last words)
was written to Trudy Schaub, his sister I believe, on 13 March 1917
Dear Trudy,congratulation to your Saint's day.
Greetings from my heart for you, Mum and Tita. See you soon, Yours Carl