Sorry for your loss.
Anyway, here is the text of the Ave Maria:
<< AVE Maria,
gratia plena, Dominus tecum.
Benedicta tu in mulieribus,
et benedictus fructus ventris tui, Iesus.
Sancta Maria, Mater Dei, ora pro nobis peccatoribus, nunc,
et in hora mortis nostrae.
Amen. >>
It's basically the latin (or Italian depending on translation) of the Catholic Hail Mary.
Unfortunately, it's not at all about angels...it's just in praise of the Virgin Mary.
As for it being by Andrea Boccelli, there are literally hundreds of musical settings for the prayer. Boccelli has no doubt performed a number of them since a lot of them are "standards" in any vocalist's repertoire. However, since he's not a songwriter, the version at your grandfather's burial will likely be one of the more popular settings by Stravinski, Verdi or Mozart, potentially a recording of Boccelli.
My personal favorite setting that I've heard is by a guy named Busto...it's quite beautiful.
Here is the translation:
<< HAIL Mary, full of grace, the Lord is with thee. Blessed art thou amongst women and blessed is the fruit of thy womb, Jesus. Holy Mary, Mother of God, pray for us sinners, now, and in the hour of our death. Amen. >>