Nobody else has been told he's coming, have they / isnt he?

We'd better not stay up too late tonight, didn't we / have we / had we?

I suppose it's time we called it a day, didn't we / isn't it / don't I?

Nobody else has been told he’s coming, have they? (have they относится к nobody).

We’d better not stay up too late tonight, had we? (had we относится к We’d better = We had better переводится как нам не следует).

I suppose it’s time we called it a day, isn’t it? (isn’t it относится к it’s time).