I think they will stick with something classy and traditional for a middle and something maybe a bit more modern for the first, but it will be fairly restrained. Nothing cre8ive for sure! They will also probably go for something that is appealing to both British and American ears.
Perhaps - [name_f]Amelia[/name_f], [name_f]Sophia[/name_f], [name_f]Eleanor[/name_f], [name_f]Olivia[/name_f], [name_m]Theodore[/name_m], [name_m]Benjamin[/name_m], [name_m]Christopher[/name_m].
They might go for something more formal but say that the baby will be known by a nickname - so [name_m]Harry[/name_m]'s full name is [name_m]Henry[/name_m] but everyone calls him [name_m]Harry[/name_m], and [name_f]Meghan[/name_f] is a middle name (her first being [name_f]Rachel[/name_f]). Perhaps - [name_m]Alfred[/name_m] ([name_u]Alfie[/name_u]), [name_m]Richard[/name_m] ([name_u]Ricky[/name_u]), [name_f]Margaret[/name_f] ([name_f]Margot[/name_f]), [name_f]Alexandra[/name_f] ([name_u]Alex[/name_u])