1) Is wishing non muslims on their festivals a Shirk? Or is it haraam in anyway?
2) What about Hindus?

by

1) No. https://www.tasnimnews.com/en/news/2019/12/25/2167414/ayatollah-khamenei-pays-tribute-to-jesus-christ-on-christmas-eve.
2) If it is confirming their shirk then it is not allowed.