I just saw this… well, my daughter [name]Vivienne[/name] [name]Grey[/name] was born in [name]January[/name], so I guess I vote for that 
I like [name]Vivienne[/name] more than [name]Vivian[/name], but [name]Vivien[/name] more than either. I find it the perfect compromise of frill to tailored. All three have wandered up and down my favourite name lists so none are really bad but I favour [name]Vivien[/name].
I do not like [name]Vivianne[/name] at all, ever.
With [name]Elena[/name], [name]Henry[/name], and [name]Oliver[/name], I’d go with [name]Vivian[/name].
I tend to prefer that spelling for first names anyways. It’s funny cause one of my combo ideas is [name]Serena[/name] [name]Vivienne[/name]. 
Anyways, I like [name]Vivian[/name] [name]Grey[/name].
Perhaps the name [name]Serenity[/name] for Nantucket peace? [name]Vivian[/name] [name]Serenity[/name] is lovely imo.
I like both spellings, but I like [name]Vivienne[/name] slightly more! I think [name]Vivienne[/name] [name]Grey[/name]/[name]Gray[/name] has a better flow than [name]Vivienne[/name] [name]Serena[/name], although I suppose it depends on your last name as well.
I, personally, think [name]Vivien[/name] goes best with your family. I think the shorter version and one with an E fits best with your other kids:
[name]Elena[/name]
[name]Henry[/name]
[name]Oliver[/name]
[name]Vivien[/name]
And I think if you go with [name]Vivien[/name] or [name]Vivienne[/name] you should use [name]Grey[/name], but if you do [name]Vivian[/name] you should use [name]Gray[/name].
As a side note, we are almost 100% sure we’re naming our daughter [name]Viviana[/name] - due in [name]July[/name]. 
Roman[/name]]I prefer [name]Vivienne[/name], but I think [name]Vivian[/name] looks best with [name]Elena[/name], [name]Henry[/name] and [name]Oliver[/name].