Learn Italian: Due escursionisti sono restati intrappolati nel bosco. - Two hikers remained trapped in the woods.

Using restare (or rimanere) instead of essere as the passive auxiliary creates the resultative passive. While sono stati intrappolati focuses on the action of them being trapped by something, sono restati intrappolati emphasizes the resulting state: they ended up trapped and were stuck there.

Could I use the verb "rimanere" instead of "restare" in this sentence?

Absolutely. In the resultative passive, restare and rimanere are virtually interchangeable. You could say sono rimasti intrappolati and it would mean the exact same thing.

Why are there two past participles here, and why do they both end in "-i"?

The phrase is built with the auxiliary essere (conjugated as sono), the past participle of the resultative verb (restati), and the main verb's past participle (intrappolati). Because the auxiliary is essere, all past participles must agree in gender and number with the masculine plural subject escursionisti.

The singular of "hikers" is "escursionista". Why does the plural end in "-i" instead of "-e"?