Congratulations!
I think [name_f]Alina[/name_f] and [name_f]Cecilia[/name_f] work really well from your list.
[name_m]Sebastian[/name_m] and [name_f]Isabella[/name_f] are both longer flowing names. So some suggestions going off of that…
[name_m]Sebastian[/name_m], [name_f]Isabella[/name_f], and [name_f]Victoria[/name_f]
[name_m]Sebastian[/name_m], [name_f]Isabella[/name_f], and [name_f]Julietta[/name_f]
[name_m]Sebastian[/name_m], [name_f]Isabella[/name_f], and [name_f]Katrina[/name_f]
[name_m]Sebastian[/name_m], [name_f]Isabella[/name_f], and [name_f]Cassandra[/name_f]
[name_m]Sebastian[/name_m], [name_f]Isabella[/name_f], and [name_f]Belinda[/name_f]
[name_m]Sebastian[/name_m], [name_f]Isabella[/name_f], and [name_u]Louise[/name_u]
[name_m]Sebastian[/name_m], [name_f]Isabella[/name_f], and [name_u]Willow[/name_u]
[name_m]Sebastian[/name_m], [name_f]Isabella[/name_f], and [name_f]Dorothy[/name_f]
[name_m]Sebastian[/name_m], [name_f]Isabella[/name_f], and [name_f]Heather[/name_f]