Not generally a fan of [name_f]Matilda[/name_f], but I think it sounds absolutely delightful with [name_u]Owen[/name_u]. I also chose [name_f]Margot[/name_f]. I think I like the fact that one starts with the same sound that the other ends with.
Madeliene and [name_f]Vivienne[/name_f] are too similar in end-sound to [name_u]Owen[/name_u] for my taste. [name_f]Mira[/name_f] & [name_f]Zara[/name_f] are more exotic choices, though honestly I’m not of the mind that sibling names should be alike in style/tone/category. If that’s important to you, something to consider.
I love [name_u]Owen[/name_u] and [name_f]Madeleine[/name_f], [name_u]Owen[/name_u] and [name_f]Vivienne[/name_f], and [name_u]Owen[/name_u] and [name_f]Margot[/name_f].
I like [name_u]Owen[/name_u] and [name_f]Phoebe[/name_f], [name_u]Owen[/name_u] and [name_f]Matilda[/name_f] and [name_u]Owen[/name_u] and [name_f]Lila[/name_f].
I love [name_u]Owen[/name_u] and [name_f]Phoebe[/name_f]! [name_m]Even[/name_m] though [name_u]Owen[/name_u] is somewhat popular it is an unexpected choice just like [name_f]Phoebe[/name_f] is. I think they are a charming sibset. I actually do know a pair of siblings named [name_u]Owen[/name_u] and [name_f]Madeleine[/name_f] though which match well but [name_f]Madeleine[/name_f] is much more common than [name_f]Phoebe[/name_f] is.