Learn Hardcore Spanish (Latin America): Proponen ascenderla y acordamos hacerlo. - They propose promoting her, and we agree to do it.

Breakdown of Proponen ascenderla y acordamos hacerlo.

Who is doing the actions in proponen and acordamos?

Spanish often leaves subject pronouns unstated when the verb ending already shows the subject.

proponen = they propose / you all propose
In most Latin American contexts, this will usually be understood as they propose.
acordamos = we agree (or sometimes we agreed, depending on context)

So the sentence has two different implied subjects:

Spanish does this all the time, so not saying ellos or nosotros is completely normal.

Why is it ascenderla instead of la ascender?

Because object pronouns can attach to an infinitive in Spanish.

Here, ascender is an infinitive, and la is a direct object pronoun attached to it:

With infinitives, Spanish normally puts the pronoun at the end as one word:

You generally would not say la ascender in standard Spanish.