Bonjour
QUESTION 2
As-tu invité les garçons ?
Oui, je les ai invités.
"Les" as a direct object pronoun replaces "les garçons" (masc.plur) so the past participle "invités" ends with an "S" as it has to agree whith the direct object, or the pronoun direct object when it is is before the passé composé
QUESTION 3
As-tu vu les filles ?
oui, je les ai vues.
"Les" replaces "les filles" (fem. plural) = past participle agree with it = "vues"
hope this helps ☺☺☺