I’m quite passionate about names but there’s a limit for me. These are individuals not pets. Kids don’t need a “theme” or matching names. If you have named one in a specific cultural or religious way, it makes sense to me continuing this way.
My LO has a traditional Irish name. It’s hardly going to be fair if I decide that I’m not going to use something Irish for LO2. Maybe my LO1 would be upset about a “complicated” (by [name_f]English[/name_f] standards) name and maybe LO2 might be left over. 
That said, worst sibset names:
Have to be careful not to out myself here
Gucci and Prada
Holden and [name_f]Mercedes[/name_f] (cars)
Holden and [name_m]Ford[/name_m] (cars)
Misspelt Irish names (Tadgh was one of them)
Twee rhyming names for girls
Scarlet and O’[name_f]Hara[/name_f] - this one might have been one singular child but she has a twin.
Scarlet and [name_u]Ruby[/name_u]
Chardonnay and something else alcohol related
Have heard this one a couple of times - Anything political for a single political party (no thank you) so 2 kids with American [name_m]President[/name_m] names in Australia, naming kids after in/famous politicians in Australia.
Naming kids after AFL (Aussie rules football players)