Learn Italian: Confermiamo che siamo favorevoli e vogliamo approvare la spesa. - We confirm that we are in favor and want to approve the expense.

To say "They confirm that they are in favor...", you must shift all the "we" verbs to "they" verbs to match the new perspective: Confermano che sono favorevoli e vogliono approvare la spesa.

Since the subject "we" does both actions, shouldn't we use di + infinitive instead of che?

Both are correct! When the subject of the main verb (confermiamo) and the reported verb (siamo) is exactly the same, Italians often use di + the infinitive verb: Confermiamo di essere favorevoli.... However, using che with a conjugated verb is also perfectly normal and is often used to make the statement sound more explicit.

Why don't we use the subjunctive mood after che here?

We generally use the subjunctive after che for opinions, doubts, or emotions (like speriamo che - we hope that). But confermare (to confirm) expresses certainty and establishes a fact. Verbs of certainty and direct reporting are followed by the standard indicative mood.

Why does favorevole end in an -i here?