'Von' is too vague for me and would hardly bear any connection to your mother's surname, IMO, since it's not the main point of a 'von der' Surname. Your son would be Miles From, not Miles Mothersurname. It'd be similar to calling him Miles Mac or Miles O if your mother's surname was MacDonald or O'Shea. Part of it's there, sure, but not the part that actually identifies the family.
I'd go with Vaughn; since between the two it's the only one that's actually a name, I prefer it.

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