Breakdown of Est-ce que tu espères que nous puissions sceller le portail afin de survivre ?
tu
you (informal singular)
nous
we / us (object pronoun)
est-ce que
is it that / do / does (question marker)
pouvoir
to be able to / can
Questions & Answers about Est-ce que tu espères que nous puissions sceller le portail afin de survivre ?
Why is puissions in the subjunctive here instead of the indicative?
Would it be completely wrong to use the indicative pouvons in this question?
Strictly speaking, yes. However, in casual spoken French, you might actually hear native speakers use the indicative (pouvons) even in a question. For your B2 level and any writing or exams, always stick to the formal rule: use the subjunctive (puissions) when espérer que is in a question or negative.
Why do we use afin de + infinitive here instead of afin que + subjunctive?
Because the subject performing both actions is the same. "We" are the ones who can seal the portal, and "we" are the ones surviving. When the subject doesn't change, French uses afin de (or pour) + the infinitive (survivre). You only use afin que + subjunctive when a new subject is introduced.
Is sceller used exactly like "to seal" in English?