Opinions on these two names?

If I were you I would try out the names and see how they look: Arnie Robin Hazel Grace or Una Fawn Hazel Grace. If I were you I would have a couple of other names picked out you know in case when the baby's born he/she doesn't look like it. See if your friends like it ask your MIL and your father - what do they think. Personally I myself love the names but you got to see if your child is a Arnie Robin / Una Fawn, you know how some people have names that match them see if your kid fits it.