If truth be told, I wasn’t the smartest person there.
It is important that they be at the wedding.

The past subjunctive is “WERE” for all persons:

I wish I were there.
If the truth were told, I would not be the smartest person there.

The past perfect subjunctive starts with “had” and takes the past participle; for “to be” it is “been”:

I wish I had been there to see that.
If the truth had been told, I would not have been the smartest person there.

There is a present perfect subjunctive which is “HAVE” for all persons plus the past participle:

I would rather he have been in the wedding.
It’s crucial that she have been in this situation before.

There you go. Now it is correct.