Learn Italian: Ho sempre sperato che loro fossero flessibili e spontanei. - I have always hoped that they were flexible and spontaneous.

The verb sperare (to hope) expresses a desire or emotion, which requires the subjunctive mood for the second part of the sentence. Because we are talking about a past timeframe, we use the imperfect subjunctive form fossero.

The main verb Ho sperato is in the passato prossimo (present perfect). Shouldn't it trigger the present subjunctive?

The passato prossimo is a flexible tense: it can trigger the present subjunctive for ongoing/future events, or the imperfect subjunctive for past events. Because the sentence refers to a past state ('that they were'), we need a past timeframe, making the imperfect subjunctive fossero the correct choice.

Why does flessibili end in -i?

The dictionary form of this adjective is flessibile. Adjectives that end in -e in the singular (regardless of whether they are masculine or feminine) always change to -i in the plural. Here, it matches the plural subject loro.

Do I have to include the pronoun loro before fossero?

It is not strictly mandatory because the verb form fossero already tells us the subject is 'they' (3rd person plural). However, including loro adds emphasis or helps clarify exactly who you are talking about if the topic of conversation just changed.