All depends on your surname, family honour names, parents names, etc - but a natural similar fit for [name_f]Florence[/name_f] [name_f]Isla[/name_f] & [name_f]Delilah[/name_f] [name_f]Mae[/name_f] (without knowing any of the other variables) for me would be:
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GIRLS:
[name_f]Florence[/name_f] [name_f]Isla[/name_f], [name_f]Delilah[/name_f] [name_f]Mae[/name_f] & [name_f]Lucinda[/name_f] [name_f]Rose[/name_f] [nn Lucy/Lucy-Rose]
[name_f]Florence[/name_f] [name_f]Isla[/name_f], [name_f]Delilah[/name_f] [name_f]Mae[/name_f] & [name_f]Wilhelmina[/name_f] [name_f]Joy[/name_f] [nn Willa]
[name_f]Florence[/name_f] [name_f]Isla[/name_f], [name_f]Delilah[/name_f] [name_f]Mae[/name_f] & [name_f]Evangeline[/name_f] [name_f]Willow[/name_f] [nn Evie]
[name_f]Florence[/name_f] [name_f]Isla[/name_f], [name_f]Delilah[/name_f] [name_f]Mae[/name_f] & [name_f]Anastasia[/name_f] [name_f]Rose[/name_f] [nn Nancy/Stacey/Tasi/Ana]
[name_f]Florence[/name_f] [name_f]Isla[/name_f], [name_f]Delilah[/name_f] [name_f]Mae[/name_f] & [name_f]Theodora[/name_f] [name_f]Ivy[/name_f] [nn Teddy/Thea]
——
BOYS:
[name_f]Florence[/name_f] [name_f]Isla[/name_f], [name_f]Delilah[/name_f] [name_f]Mae[/name_f] & [name_m]Caspian[/name_m] [name_m]James[/name_m] [nn Caspy]
[name_f]Florence[/name_f] [name_f]Isla[/name_f], [name_f]Delilah[/name_f] [name_f]Mae[/name_f] & [name_m]Wilfred[/name_m] [name_m]Otto[/name_m] [nn [name_m]Freddie[/name_m] or Will/Wilf]
[name_f]Florence[/name_f] [name_f]Isla[/name_f], [name_f]Delilah[/name_f] [name_f]Mae[/name_f] & [name_m]Everett[/name_m] [name_m]Oscar[/name_m] [nn Evan/Ever]
[name_f]Florence[/name_f] [name_f]Isla[/name_f], [name_f]Delilah[/name_f] [name_f]Mae[/name_f] & [name_m]Malachi[/name_m] [name_m]Jude[/name_m] [nn Kai]
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Those are just my gut feeling suggestions! Longer, flowing, elegant first names with lots of L and F and E sounds and shorter, simple but cute and nature-y middle names