Obviously, the names of my characters are extremely important in the story. In this case, for this story, I have the setting in a fantasy kingdom, in the past, in which magic exists. There are four siblings, who’s names aren’t exactly traditional. What are your thoughts?
Sordicus
Corinthina/Blumera/Blumeria (any decide on this one. The latter two remind me of flowers and she has a magical influence on plants)
Josella
Nadronicei (nay-drone-eh-cai)
Are these to “out there”? Does anyone have better suggestions?
I feel like the last one is too out there. Maybe take off the cai syllable. Also, Spordicus sounds really similar to [name_m]Spartacus[/name_m]. It would help if there were character descriptions.
I’d say they’re all fine… just very long. And that last one might trip people up. I know it tripped me up.
You don’t want the names to distract from the story. I think that they can be different or made up even, but they should be pronounce-able. Blumeria is lovely for a nature name, it’s simple and clean and I can easily read it. Josella isn’t bad, but it’s a little more “normal” sounding. Nadronicei, even with your phonetic spelling, I’m still lost on how to say it. Here are a few suggestions that may be helpful in getting the sounds you like with a more reader friendly appeal.
Zechias
I’m keeping Blumeria, I love it. 
Joza
Nordikai
It may be helpful knowing a little something about the siblings so, like Blumeria, the name would fit.
I love them all, except the last one is kind of a stumbling block. It’s hard to read–but plenty of people have hard to pronounce names in their stories. Take the Eragon series for example; the names are crazy. if you like the name, go for it.
Personally, I think Corinthina is better than the latter two, although you might want to shorten it to Corinthia. Blumera and Blumeria are just…I don’t know. They sound pretty when you say them, but they don’t look all that pretty. If someone pronounced it Bluhm-era instead of Bloom-era, than it kind of sounds ugly. So you may want to change to spelling to Bloomera (which is lengthier, but also more directly related to plants), or just go with Corinthia/Corinthina.