Like the genie trio landorus, thundurus, and tornadus
No, because they're from different Generations. Mew is Gen I, Jirachi is Gen III and Celebi is Gen II.
Trios are Pokemon like Kyurem, Reshiram and Zekrom which are from the same Generation and the same region. Usually they will be referred to as a trio in the anime.
List of Legendary Trios