Question

Kalo 'They were really scared' itu passive gak?
terus, kalo 'the snakes would bite them' itu termasuk simple past future gak?

Answer 1

They were really scared termasuk passive, simple past tense. :)
passive itu to be + past participle (V3) :)

The snakes would bite them termasuk past future karena rumusnya past future itu S+should/would+verb

btw, orang2 native speaker kenal past future sebagai "future in the past"
buat infomu aja :D