The verb "a trebui" is impersonal and to conjugate it in the indicative present form you just use "trebuie" for all the persons in singular and plural. You only have to pay attention to the verb following "trebuie", because that should be conjugated according to the subject. In this case: (noi) să tăcem.
This is a difficult topic even for Romanians. You can find the forms of "A trebui" at conjugare.ro , yes it has personal forms such as "noi trebuim" but to use this form "we" must be the subject of the need. "Noi le trebuim lor" = "they need us". In 99% of the spoken language cases "trebuie" is impersonal and intransitive ("it is needed").