The Greek text (Mat 13:32) reads:
"Which (ho) smaller than (microteron) indeed (men) is (estin) all (panton) of the seeds (spermaton)"
It couldn't be clearer or more definitive. It's not about English grammar. It's about English translations. The NIV actually adds a word—that's not in any of the manuscripts—in order to remove the conflict! The NIV reads:
"Though it is the smallest of all your seeds"
The length some people will go to remove any possible discrepancies form the Bible doesn't stop at falsifying the text, even Christ's own words! And the NIV is really good at that!
Granted, I don't know Aramaic, but in Hebrew the superlative is expressed by definite article + adjective
We have no record in Aramaic and retro-translating is a dangerous business (we know that from Textus Receptus!). The Gospels were written in koine Greek. That is the original language, regardless of what language Jesus spoke. Matthew, an eyewitness, says in Greek what Jesus said.
I thought it was generally accepted (on internal evidence) that Matthew's gospel was orignally written in Aramaic, though no Aramaic copy is known to survive.
Personally, I'd be hesitant about too close-nitpicking in any ancient language. Lord knows there are enough current misunderstandings and confusion and misinterpretation among actual speakers of the same language at the same time in the same geographical area.