I love the idea of honouring your brother through both middles - and I also think it can be a bit heavy having an honour name as the first name; I prefer the first name to be the child’s own.
I can see why you’re hesitant on Poet. I love the sound and symbol too but it does make it a little harder for the wearer if they’re not in the arts - or in a celeb community!
Some names that still have the whimsical feel but less prescriptive perhaps:
Poem
Ever
Atlas
Joss
Leif
Jude
Micah
Aven (someone on here just posted this!)
Sorrel
Heath
Emrys
Marlo
Hollis
Rainer (after the poet, not rain)
Indigo
Conrad
Cyrus
Cosmo
Casper
Hartley
Jasper
Rafferty (Raffy/ Raffa)
Phoenix
Sterling
Zephyr
Jarlath
Ziggy
Kai
Edit: also you could experiment with Blue and then other bird names for the middle depending on flow. Eg Joss Cardinal or Rafferty Blue.
But I also think if Poet speaks to you the most, you should use it. I like it! Names are less and less conventional - thank goodness (or everyone still called the 90s names suggested in first post!) - and a Poet lawyer will appear before a Blossom judge.