Being a twin, I deeply appreciate that my name is distinctly different from my twin's name. Here are some aspects that come to my mind. Choose similar-sounding names if you want these aspects; avoid similar-sounding names if you don't:
Pros of similar-sounding names
- can be easier to say quickly, i.e. they flow naturally from the tongue.
- emphasize that they belong together, they are a set, they are part of the same family.
Cons of similar-sounding names
- risk of teasing.
- risk of feeling less distinct, harder to define oneself without referring to the sibling.
I might add more bullets to either list when I think of more.
Writing this answer makes me think that we could also have a question about general factors that could be considered when trying to come up with names for children -- but that's unrelated to this question.