We need some middle name inspiration to go with Callum. We only want one middle name. These are the ones we are considering, but don’t know if they sound just right.
Callum David
Callum Dean
Callum Rhys
Side note, older brother’s name is Eoin Robert, so that middle is already taken.
Of the three, I like [name_u]Callum[/name_u] [name_u]Rhys[/name_u] the best.
Here are a few more ideas: 
[name_u]Callum[/name_u] [name_f]Winslet[/name_f]
[name_u]Callum[/name_u] [name_m]Faris[/name_m]
[name_u]Callum[/name_u] [name_u]Lux[/name_u]
[name_u]Callum[/name_u] [name_u]Orion[/name_u]
[name_u]Callum[/name_u] [name_u]Murray[/name_u]
[name_u]Callum[/name_u] [name_u]Hayes[/name_u]
[name_u]Callum[/name_u] [name_u]Reid[/name_u]
[name_u]Callum[/name_u] [name_u]Gray[/name_u]
[name_u]Callum[/name_u] [name_u]West[/name_u]
[name_u]Callum[/name_u] [name_m]Hewitt[/name_m]
[name_u]Callum[/name_u] [name_m]Gates[/name_m]
I love all three goodness!
I think [name_u]Callum[/name_u] [name_m]David[/name_m] or [name_u]Callum[/name_u] [name_u]Dean[/name_u] would fit best with his brother but [name_u]Callum[/name_u] [name_u]Rhys[/name_u] is lovely as well!
[name_u]Callum[/name_u] [name_u]Rhys[/name_u] is wonderful
Some suggestions
[name_u]Callum[/name_u] [name_u]Jonah[/name_u]
[name_u]Callum[/name_u] [name_m]Arthur[/name_m]
[name_u]Callum[/name_u] [name_m]Peter[/name_m]
[name_u]Callum[/name_u] [name_u]Jude[/name_u]
[name_u]Callum[/name_u] [name_m]Silas[/name_m]
[name_u]Callum[/name_u] [name_m]Isaac[/name_m]
I like [name_u]Callum[/name_u] [name_u]Dean[/name_u] a lot.
Ross was the first thing that came to mind. Callum Ross but out of yours my favourite is Callum Rhys!
I like [name_u]Callum[/name_u] [name_m]David[/name_m]!
The ones you already have are really beautiful,Callum [name_u]Dean[/name_u] and [name_u]Callum[/name_u] [name_u]Rhys[/name_u] are my favourites
[name_u]Callum[/name_u] [name_m]Edward[/name_m]
[name_u]Callum[/name_u] [name_m]Andrew[/name_m]
[name_u]Callum[/name_u] [name_u]James[/name_u]
[name_u]Callum[/name_u] [name_u]Oliver[/name_u]
[name_u]Callum[/name_u] [name_u]Wyatt[/name_u]
[name_u]Callum[/name_u] [name_u]Robin[/name_u]
[name_u]Callum[/name_u] [name_u]Tristan[/name_u]
[name_u]Callum[/name_u] [name_u]Hayden[/name_u]
[name_u]Callum[/name_u] [name_m]Maxton[/name_m]
[name_u]Callum[/name_u] [name_u]Riley[/name_u]
[name_u]Callum[/name_u] [name_m]Leo[/name_m]
[name_u]Callum[/name_u] [name_m]Ethan[/name_m]
[name_u]Callum[/name_u] [name_u]Flynn[/name_u]
[name_u]Callum[/name_u] [name_u]Finn[/name_u]
[name_u]Callum[/name_u] [name_m]Xander[/name_m]
[name_u]Callum[/name_u] [name_u]Everett[/name_u]
[name_u]Callum[/name_u] [name_u]August[/name_u]
[name_u]Callum[/name_u] [name_u]Auden[/name_u]
[name_u]Callum[/name_u] [name_u]Aidan[/name_u]
[name_u]Callum[/name_u] [name_u]Liam[/name_u]
[name_u]Callum[/name_u] [name_u]Noah[/name_u]
[name_u]Callum[/name_u] [name_u]Dorian[/name_u]
[name_u]Callum[/name_u] [name_u]Greyson[/name_u]
[name_u]Callum[/name_u] [name_u]Callum[/name_u] [name_m]Aldridge[/name_m]
[name_u]Callum[/name_u] [name_u]Jameson[/name_u]
[name_u]Callum[/name_u] [name_m]Graham[/name_m]
[name_u]Callum[/name_u] [name_u]Eli[/name_u]
[name_u]Callum[/name_u] [name_u]Connor[/name_u]
[name_u]Callum[/name_u] [name_m]Matthew[/name_m]
[name_u]Callum[/name_u] [name_u]Rory[/name_u]
[name_u]Callum[/name_u] [name_u]Blake[/name_u]
[name_u]Callum[/name_u] [name_m]Nicholas[/name_m]
[name_u]Callum[/name_u] [name_m]Nathaniel[/name_m]
[name_u]Callum[/name_u] [name_u]Jonah[/name_u]
[name_u]Callum[/name_u] [name_m]Silas[/name_m]
[name_u]Callum[/name_u] [name_u]Beau[/name_u]
[name_u]Callum[/name_u] [name_m]Charles[/name_m]
[name_u]Callum[/name_u] [name_u]Ryder[/name_u]
[name_u]Callum[/name_u] [name_m]William[/name_m]
[name_u]Callum[/name_u] [name_u]Easton[/name_u]
[name_u]Callum[/name_u] [name_u]Evan[/name_u]
[name_u]Callum[/name_u] [name_u]Noel[/name_u]
[name_u]Callum[/name_u] [name_m]Atticus[/name_m]
[name_u]Callum[/name_u] [name_m]Garrett[/name_m]
[name_f]My[/name_f] first thought was [name_u]Callum[/name_u] [name_u]Rhys[/name_u] for flow
However [name_u]Callum[/name_u] [name_m]David[/name_m] goes really well with [name_m]Eion[/name_m] [name_u]Robert[/name_u]
I adore [name_u]Callum[/name_u] [name_u]Dean[/name_u] too but when I say it fast it feels like it runs together
Ultimately I think I would go with [name_u]Callum[/name_u] [name_m]David[/name_m]
I like [name_u]Callum[/name_u] [name_u]Rhys[/name_u] the best out of your list!
[name_u]Callum[/name_u] [name_m]Dennis[/name_m]
[name_u]Callum[/name_u] Douglar
[name_u]Callum[/name_u] [name_u]Nolan[/name_u]
[name_u]Callum[/name_u] [name_u]Scott[/name_u]
[name_u]Callum[/name_u] [name_m]Tobias[/name_m]
[name_u]Callum[/name_u] [name_m]Josiah[/name_m]
[name_u]Callum[/name_u] [name_m]Preston[/name_m]
[name_u]Callum[/name_u] RHett
[name_u]Callum[/name_u] [name_m]Victor[/name_m]
[name_u]Callum[/name_u] [name_u]Regan[/name_u]
[name_u]Callum[/name_u] [name_m]Ethan[/name_m]
[name_u]Callum[/name_u] [name_u]Wesley[/name_u]
[name_u]Callum[/name_u] [name_m]Victor[/name_m]
[name_u]Callum[/name_u] [name_m]Franklin[/name_m]
[name_u]Callum[/name_u] [name_m]Ian[/name_m]
[name_u]Callum[/name_u] [name_m]Lewis[/name_m]
[name_u]Callum[/name_u] [name_u]Percy[/name_u]
[name_u]Callum[/name_u] [name_m]Xavier[/name_m]
[name_u]Callum[/name_u] [name_u]Everest[/name_u]
[name_u]Callum[/name_u] [name_u]Jackson[/name_u]
[name_u]Callum[/name_u] [name_m]Ezekiel[/name_m]