Is it possible to show the leaderboard for a group of users, for example friends or colleagues using a list of user IDs?
It's quite easy to generate an all-time leaderboard using the Stack Exchange Data Explorer. As an example, I have compiled a list of user IDs from Stack Exchange staff (via this method) and used that for a Meta Stack Exchange leaderboard for this group:
Note that SEDE is updated once a week, on Sunday morning (but the leaderboards aren't real-time either). SEDE is worse at compiling weekly/monthly leaderboards, that requires complicated queries similar to this one.