Officiant help! (catholic officiant, non-religious couple)

The “get ordained” is a online thing through a universalist church. If your grandfather is committed to his faith, I’d expect he’d balk at this idea for 2 reasons - getting ordained in a church other than his own and his faith believe marriage should be a sacrament which he would be aiding you in something against his faith.

In order to marry a couple in the Catholic Church, the officiant must be a Priest or Deacon. You aren't getting married in the church so he would not be able to marry you with either of those titles. If he wishes to legally be able to officiate weddings (like yours) without the religion aspect, I don't see why that would be an issue since you aren't getting married in a church. If he is a religious man he may not be on board with it though.

One thing you could do to incorporate your grandfather is to have someone else marry you legally but perhaps have him share some words of marriage wisdom during the ceremony.

Anyone can get ordained online it just isn't done through an actual Church. If you're not getting married in a church religious choice doesn't matter

If your grandfather is very religious, yes, he will probably balk at the idea of being "ordained," because in the Catholic Church, ordination is a sacrament and taken very seriously. You could bring it up to him, I just would not be surprised if he says no.