Personally, I prefer [name_m]Rhett[/name_m] [name_m]Nathaniel[/name_m] and [name_f]Lucille[/name_f] [name_f]Elizabeth[/name_f]! The individual names flow better than those in the first set, and [name_m]Rhett[/name_m] and [name_f]Lucille[/name_f] sounds more like siblings.
I think [name_f]Cora[/name_f], [name_f]Marigold[/name_f], and [name_m]Benen[/name_m] stylistically match each other better than [name_m]Rhett[/name_m] and [name_f]Lucille[/name_f]. Personally, I would substitute [name_m]Benen[/name_m] with [name_m]Benjamin[/name_m] or [name_m]Bennett[/name_m], since those fit better with classics like [name_f]Cora[/name_f] and [name_f]Marigold[/name_f]. [name_m]Rhett[/name_m] and [name_f]Lucille[/name_f] sound good together as well.