You got it backward... The Eldar were created by the Eldar Pantheon. They were Isha's creation hence why the Gods started killing each other (More just Khaine but whatever) as Khaine was told his death would come at the hands of the Eldar and because of this decided fuck the Eldar. Isha didn't like that so she had some way to communicate with them after Asuran or whatever the fuck the high Eldar God's name is said to leave the Eldar alone. Khaine found out was fucked off took Isha prisoner or something, Vaul was annoyed decided to make a deal with Khaine which was to give him 100 blades hence the term Blade of Vaul comes from but Vaul didn't make 100 and so threw in a couple of identical blades that were shit, Khaine didn't realise till they'd fucked off and some more shit happened I can't remember. But yeah Eldar were made by the Gods... Apparently...
Pretty bird. So there you go, Eldar didn't create their Gods. The Old Ones are rumoured to be Eldar Gods.
No!........Yes?........I am so confused...... Ok of more time. The Eldar were created by the Old Ones. Just like the orks in order to put down the rebellion the necrontyr were giving. Using the Realm of souls they created gods for whatever they needed at the time using their emotions. During which we started to lose our way and then came the fall. During which the ability to create new gods became lost to history.