French language Q&A Forum

In the writing challenge "Les noces d'or de mes grands-parents" the phrase "Et ce qu'ils se sont déclaré était tellement émouvant" appears. Why is there no plural agreement on the verb "déclaré "?

It sees to be the same case as this example in the lesson "Conjugate reflexive verbs (+être) in Le Passé Composé (conversational past)":

Elles se sont disputées = They had an argument.

Is it because the verb has an object which precedes it and the rule of agreement with a prior object takes precedence over the rule of agreement with the subject?

Something like case 3 1/2 here:https://www.lawlessfrench.com/grammar/agreement-with-pronominal-verbs/

In the writing challenge "At Uncle Robert's 70th birthday" we are asked to translate "when I'm done with all that".

The suggested answers both use "en". E.g. "quand j'en aurai fini avec tout cela".

I wonder why "en" is required? I expect it to replace "de qqch" but in this sentence isn't that role - specifying what is being finished - supplied by "avec tout cela"?

Is there a lesson on Kwiziq that gives an example of this usage? It is not really included in En can replace de + [phrase] (French Adverbial Pronouns)

The lesson states that the e in, for example, 'joueront' is not pronounced.

Please explain why this is so when the verb in the following sentence, taken from the lesson, the e is pronounced.:

Nous volerons dans une heure.