[name]Jack[/name] and [name]Hallie[/name] are great sibling names. Here are my opinions on your list.
[name]Pearl[/name] - Probably the best “fit” with [name]Jack[/name] and [name]Hallie[/name]. [name]Pearl[/name] [name]Audra[/name] [name]Jane[/name] is lovely!
[name]Willa[/name] - Not my cup of tea and it shares too many l’s with [name]Hallie[/name] and I’m not too crazy about the sound with [name]Audra[/name]
[name]Dulcie[/name] - All I see and hear is the word “dull” and it’s too rhymey with [name]Hallie[/name] and clashes with [name]Audra[/name]
[name]Bridget[/name] - My second choice and it has a great nn of [name]Bree[/name]. [name]Bridget[/name] [name]Audra[/name] [name]Jane[/name] is spunky!
I think [name]Bridget[/name] stylistically goes great with [name]Jack[/name] and [name]Hallie[/name], spunky with a [name]Brit[/name]/Irish vibe. [name]Pearl[/name] [name]Audra[/name] [name]Jane[/name] is sooo pretty! I think either would be nice.