I really like them both.. Hmm... A siblings or twins... Idk. As siblings, I'd probably have one, then have another kid with a completely different name, and then use the other [ie... Have
Silas, then
Maria, then
Silvia]. Not that it's easy to control that. :P
I would spell
Silvia as
Sylvia though.
Silvia reminds me a bit of saliva spelled that way.