1) Is it possible for a moderator to restore comments that are deleted by another moderator?
2) Also, are comments that are deleted by owners themselves be restored likewise by any of the three moderators?
1) A Moderator can undelete comments which are deleted by other Moderators. A Mod may undelete comments deleted by other mod with or without edits if it is relevant to the post.
2) Moderators can't undelete comments which are deleted by users (their own comments). Mods also can't undelete comments of deleted users . Same way, they also can't move comments of deleted users to chat. Mods also can't undelete comments which are removed through flags without their intervention but they can see all these deleted comments.