I love [name]Ophelia[/name] and [name]Octavia[/name] for girls names, but what would be good nicknames for them?
Brother’s name is [name]Caspian[/name].
I love both [name]Ophelia[/name] and [name]Octavia[/name] (and [name]Caspian[/name]), but I don’t know if I’d be brave enough to ever use them! I hope you get to! 
[name]Ophelia[/name]: Phe, [name]Fifi[/name], Phia, [name]Lia[/name], [name]Ollie[/name], Phela
[name]Octavia[/name]: [name]Tavie[/name], [name]Tavia[/name], [name]Taya[/name], [name]Vivi[/name], [name]Tay[/name], [name]Via[/name]
I [name]LOVE[/name] [name]Ophelia[/name]- it is high on my list as well- my favourite nn is Fi- I just think it is adorable. As for [name]Octavia[/name], I like the suggestion of [name]Vivi[/name]- very sweet.
Yes, fab name choices! I also love both [name]Ophelia[/name] and [name]Octavia[/name] but am too shy to use. 
I think irisrose covered all the good nicknames.
I love [name]Ophelia[/name] and [name]Octavia[/name]! My favorite nicknames for both:
[name]Ophelia[/name]: O, [name]Fee[/name]/Phee, [name]Fia[/name]/Phia, [name]Ollie[/name]
[name]Octavia[/name]: [name]Tavi[/name] ([name]Tay[/name]-vee), [name]Avie[/name], Vee, [name]Via[/name], Tave.
[name]Hope[/name] that helps!
I really, really love the nickname [name]Via[/name] (and [name]Octavia[/name] is my favorite name ending in via) the above posters pretty much said all the possible nicknames the only one I can add is [name]Octavie[/name].
But as someone who has really considered this name the nicknames Id use would be [name]Via[/name] (obviously), occasionally Vee & [name]Taye[/name], and even more occasionally [name]Tavia[/name] & [name]Tavie[/name].
For [name]Ophelia[/name] its a tad forced but I can see [name]Elia[/name] & [name]Philly[/name] happening; I think Id mostly use Fi, O & [name]Lee[/name]/[name]Leigh[/name] maybe Fi-[name]Lee[/name] as a pet name
[name]Ophelia[/name]: [name]Elia[/name] (like the trendy [name]Ella[/name], but less so), Ophie, [name]Fifi[/name], [name]Lia[/name], [name]Leah[/name]
[name]Octavia[/name]: [name]Via[/name], [name]Tavia[/name], [name]Tavi[/name], Ovie