[name]Audrey[/name] and [name]Oliver[/name] are beatiful names. I personally would stay away from more vowel names. Here are some names that I think would go great with your current names:
[name]Katherine[/name]/[name]Catherine[/name] nn [name]Kate[/name]/[name]Cate[/name]
[name]Grace[/name] (same GR sound as [name]Greta[/name])
[name]Clare[/name] (I think this sounds so lovely with [name]Audrey[/name])
[name]Simon[/name]
[name]Matthew[/name]
[name]James[/name]
(I think all these boys names would go well with [name]Henry[/name] or [name]Alexander[/name] as mn if you really like those names).
If you want to stick with vowels, I think that [name]Edward[/name] and [name]Isaiah[/name] are nice boy names, and [name]Emma[/name], [name]Emmeline[/name] or [name]Isabel[/name] are great for girls.