Which is your favorite with older siblings [name]Oliver[/name], [name]Iris[/name] & [name]Miles[/name]? We also have angel daughters named [name]Alice[/name] and [name]Lily[/name].
[name]Caspian[/name]
[name]Felix[/name]
[name]Sebastian[/name]
[name]Simon[/name]
[name]Tobias[/name]
[name]Viggo[/name]
My favourite from your list is [name]Sebastian[/name]. I think it goes really well with [name]Oliver[/name], [name]Iris[/name] and [name]Miles[/name]. (second fav is [name]Felix[/name]). Good names!
I have to agree, I like [name]Sebastian[/name]!
[name]Felix[/name] and [name]Sebastian[/name] sound the best. I like [name]Felix[/name] better personally, but [name]Sebastian[/name] is great.
I think [name]Felix[/name] and [name]Simon[/name] sound the best with your other children.
[name]Simon[/name] and [name]Sebastian[/name] are two of my personal favs. I like [name]Tobias[/name] too just not as much as [name]Simon[/name] and [name]Sebastian[/name].
[name]Caspian[/name] is nice but might stand out too much with your other children’s names.
[name]Viggo[/name] just reminds me of the actor.
I like [name]Felix[/name] best. [name]Caspian[/name] seems to fit too but [name]Felix[/name] is shorter like all your other children’s names.
I like [name]Felix[/name]. I think it flows best with your other children’s names. All your choices are nice, although I’d avoid [name]Tobias[/name] because it leaves [name]Oliver[/name] as the only sibling without the s ending.
[name]Sebastian[/name] gets my vote
[name]Sebastian[/name] sounds the best to me, shortly followed by [name]Simon[/name]. Not a huge fan of [name]Caspian[/name] (reminds me of the Chronicles of [name]Narnia[/name]!)
Before I even saw the inside of your post, my thoughts were [name]Simon[/name] and [name]Felix[/name]!
Very much like: [name]Felix[/name]
Also sounds good with siblings: [name]Sebastian[/name]
Blends in almost too much: [name]Simon[/name]
Rhymes (sort of) with [name]Iris[/name]: [name]Tobias[/name]
Out of sync with siblings: [name]Viggo[/name]
Guilty pleasure: [name]Caspian[/name] 
[name]Love[/name] your kids’ names!
I’d go with [name]Felix[/name], [name]Sebastian[/name] or [name]Viggo[/name].