I don't think you have to stick to the two middle names if you don't think it flows right. May Belle is only two syllables so in a way, May Belle and Michael match perfectly!
On the other hand, each of your boys names are two syllables, as is the middle name Michael, and the last name Taylor. I would avoid all the names being the same number of syllables because that makes it sound like a drum beat to me: Nathan Michael Taylor. BUM bum BUM bum BUM bum. Hear it?
So I think if you go with a two syllable first name, I would either do the double middle since Anthony breaks up the pattern, or just use Anthony as the middle. Nathan Michael Anthony Taylor. Hear how that breaks up the drum beat? Or even Nathan Anthony Taylor.
Anyway, just my 2 cents. If I were you, I'd do either
Nathan Michael Anthony Taylor
or
Nathan Anthony Taylor