I like
Jack but only as a nn.
Oliver is lovely but
Ollie isn't, so it's a risk.
Ellie could be anything and therefore feels more like nothing. And the thought of
Ellie and
Ollie isn't pleasant!
Georgie, like
Ellie, would benefit from a longer version as the official name. I'd go for
Georgina myself, but
Georgia would do just fine.
Vivienne won't get a French pronunciation, even in New Orleans, so I'd prefer
Vivien; but it's a name in good standing. Wells (f)? Really? How very odd.