[name_f]Catherine[/name_f] has a lot of variants - if you don’t want all three names to end in -n, what about using one of those? [name_f]Gwen[/name_f] [name_f]Caterina[/name_f] is pretty.
For boy names, I think you should consider adding to your list:
[name_m]Cameron[/name_m]
[name_m]Callum[/name_m]
[name_m]Corbin[/name_m]
[name_m]Booker[/name_m]
[name_m]Soren[/name_m]
and then use [name_m]George[/name_m] as the middle. [name_m]George[/name_m] goes well as a middle name with nearly any first name in my opinion.