What I came up to with verse #6 is

Be sure to take for truth that it'd been thus heard*
That God could not make her more a mother
He who was her father was born to her today
And he who raised her claims to be her son.

* could someone lend a hand on this "que ansina lo oyera"? Which is word to word "that thus it (object, not subject)... had heard/would hear" (at that time the subjunctive imperfect in -ra more often was what today is an indicative pluperfect, nowadays it's used in literature, I never heard it used in everyday life but I'm not the Spanish speaking world all by myself)

Q, could this mention about Spanish, Catalan and Portuguese mean that there are songs in Spanish, others in Catalan and others in Portuguese and not that all songs are in the three languages? Some songs (4) are indeed in Catalan and one in Galician -which is a Portuguese dialect and not a Spanish one though Galicia is now in Spain