lo avrebbero fatto

they would do it

→ lo
phrase Rare #35,001
they would do it Used for reported future-in-the-past: someone said or promised that they would do something. Literally, it can also mean “they would have done it” in a conditional context.
IT: Se avessero avuto più tempo, lo avrebbero fatto.
EN: If they had had more time, they would have done it.

Perché lo avrebbero fatto?

Why would they do that?

— Manon delle sorgenti (1986)

Tom e Mary hanno promesso che non lo avrebbero fatto.

Tom and Mary promised they wouldn’t do it.

Hanno detto che lo avrebbero fatto domani.

They said they would do it tomorrow.

Tom e Mary mi hanno detto che lo avrebbero fatto.

Tom and Mary told me they would do it.

Tom e Mary ci dissero che lo avrebbero fatto.

Tom and Mary told us they would do it.

Tom e Mary promisero che non lo avrebbero fatto.

Tom and Mary promised they wouldn't do it.