Can Anyone Answer this Question about the ‘New’ Mass?

Having just presided at a Mass, I have a question about the new translation.  And this is a sincere question: I’m somewhat puzzled about whether a particular feature is an error in the translation, a typo or some part of the Latin translation that I don’t understand.  I noticed it when I read the Collect for the Third Sunday of Advent, which I decided to practice since I’m celebrating Mass at our local Jesuit church that Sunday.  The Collect reads:

O God, who see how your people faithfully await….

Who see?  Shouldn’t it be “who sees”?  Is God plural?  Are the translators referring to the Trinity? 

I thought it might be a mistake in the edition of the missal I’ve been using (from the Catholic Book Publishing Corp.) but this morning I noticed the same locution in “Give Us This Day,” the daily prayer resource from Liturgical Press.  (And I thought: there’s no way that both Catholic Book Publishing and Liturgical Press got it wrong.) 

Then tonight I stumbled over this familiar part of the Mass:

Lord Jesus Christ, who said to your Apostles: Peace I leave you, my peace I give you, look not on our sins, but on the faith of your Church, and graciously grant her peace and unity in accordance with your will. Who live and reign for ever and ever.

Live and reign?  Shouldn’t it be “lives and reigns”?  Jesus Christ is certainly singular. 

I asked several Jesuit priests in my community who know Latin, and they scratched their heads.  My best guess is that it’s a Latin-based problem, or that it’s a way of addressing the Trinity, but it certainly made it difficult not to feel that the priest is making a grammatical mistake by saying “O God, who see…” and “Lord Jesus Christ…Who live and reign for ever and ever.” 

Can anyone explain what seems, at least on the surface, to be a grammatical mistake?  Thanks in advance.