Okay you got some interesting ideas but you're missing some "body" on each tracks, what I mean by that :
Sad - You have no motion, the legato strings, choirs and guitar are always playing the same pacing and same thing at almost the same range, you need some dynamics or change some tone from time to time and a constant melody that you can reuse in the same song doing some arrangement
Happy - You have mostly pluck instruments, a pizz violins, vibraphone and a sax doing almost the same thing for 4 mins, after 1 min max you need to change and go somewhere change some chords to make it move a little bit more and add something in the instruments what will add some "body" again to the song like a bass add elements to your drums track and make it more alive.
Memory - Sounds like you basically mixed Sad and Happy together. so same thing apply for this.
Relax - Same thing as Memory but with more happy in there, you started to get the idea of motion in this one a little more than the other.
You did a good job while being limited.