The correct answers are The stolen painting is thought to have been destroyed by the thieves. and The mastermind is expected to be sentenced tomorrow morning.

In C2-level English, "double passives" (a passive verb followed by a passive infinitive) are perfectly acceptable with reporting verbs or verbs of expectation (like thought, expected, believed, said).

However, verbs of effort, attempt, or beginning (like try, attempt, begin) create grammatically unacceptable double passives. Instead of "was tried to be recovered," we must use an active infinitive ("They tried to recover...") or a noun phrase ("An attempt was made to recover...").