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You've dug yourself a hole there with the two-syllables-starting-with-vowel rule. The main trick used in many places for distinguishable character names is to have them start with different sounds...
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/44615 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
You've dug yourself a hole there with the two-syllables-starting-with-vowel rule. The main trick used in many places for distinguishable character names is to have them start with different sounds. And you've just cut that selection down to about 20% of the vocabulary... Names, in real life as in stories, are there to distinguish people (and things) from each other. As such they are rarely too similar to each other. Any system or rule that enforces too close similarity would be abandoned as useless. Whenever such a system was artificially upheld (e.g. royal names in the same lineage, where traditionally people were often named after fathers, grandfathers, etc.) you had **added discriminators**. John I, "the cruel" and John II, "the great" and John III, "the conqueror". Your characters might have actual names, which are confusingly similar, and also nicknames which are more often used.