Learn Italian: Parecchie infrastrutture stanno venendo ampliate. - Several infrastructures are being expanded.

This is the progressive passive. It combines stanno (from stare, matching the subject) with venendo (the gerund of venire, acting as the passive auxiliary) and the past participle ampliate (expanded). It emphasizes an ongoing action being done to the subject.

Could I say 'stanno essendo ampliate' to mean 'are being expanded'?

No, and this is a common trap for English speakers! To express that something is currently being done, Italian uses the gerund of venire (venendo), never the gerund of essere (essendo). The combination stanno essendo is strictly incorrect in Italian.

Why does the past participle end in '-e' (ampliate)?

In all passive voice constructions, including this progressive one, the past participle must agree in gender and number with the subject. Since the subject infrastrutture is feminine plural, the participle changes from its default ampliato to ampliate.

What is the exact nuance of parecchie compared to molte or alcune?