What are the Halachos of giving presents and gifts during the year of Aveilos? Can one give a birthday present to a sibling? An appreciation gift to coworkers?

One should avoid giving presents during the year of “Aveilus” on a parent.

However if it is given as remuneration it is permissible, for example, a student to a teacher at the end of school year, husband to wife in honor of Yom Tov, or Chosson to Kallah.