It is a far different thing to hold that "sin is . . . God's creation" than it is to hold that God decreed that sin should happen and providentially bring it to pass.
What is the difference ?

God is NOT the "Author of sin
well lets look at the definition of author= The writer of a book, article, or other text.
One who practices writing as a profession.
One who writes or constructs an electronic document or system, such as a website.
An originator or creator, as of a theory or plan.
Author God.
This latter definition hits the nail on the head...

God is the author of sin , that is sin found it`s origin in the sovereign will of God.

Sin does not emante from within the essence and Intrinsic Being of God, however it does emanate from within His sovereign purpose and good pleasure...He created sin , He decreed the fall of adam for His purpose.

created beings, both angelic and human are the authors of sin and responsible for it.
Hold on there, thats attributing a little too much power to mere creatures don`t you think ? If what you mean is that they author sin by being its creator , thats dead wrong , God created all things , wether it be good or evil
Isa 45: 7 I form the light, and create darkness: I make peace, and create evil: I the LORD do all these things.

Job, a man with an anointed understanding said job 2: 10
But he said unto her, Thou speakest as one of the foolish women speaketh. What? shall we receive good at the hand of God, and shall we not receive evil? In all this did not Job sin with his lips. see also job 42: 11 Then came there unto him all his brethren, and all his sisters, and all they that had been of his acquaintance before, and did eat bread with him in his house: and they bemoaned him, and comforted him over all the evil that the LORD had brought upon him: every man also gave him a piece of money, and every one an earring of gold.

Now if what you mean is that men are morally accountable for their acts of sin, I agree. But even mens acts of sin find their origin in and by the sovereign will of God ! Aprime example is in acts 2:23Him, being delivered by the determinate counsel and foreknowledge of God, ye have taken, and by wicked hands have crucified and slain:

All the historic Reformed Confessions and Catechisms are very clear on this matter in stating that "God is not the author of sin", albeit He decreed that sin should come into the realm of the angelic host and all mankind.

I have read some of those creeds and confessions and a lot of them are reluctant to admit that God created Sin for His purpose and for His Glory.

here is a simple definition for create= To cause to exist; bring into being.