Que En paz descanse, for a formal person (elderly, authority), or que en paz descante for a friend or familiar person. It is just general - Que descanse en paz, or Que en paz descanse. It is not...
valle en paz
signo de paz
If you mean someone is resting then it's "descanso". If you mean someone is substracting then it's "restando".
"aunt" in Spanish is "tía"