Beings like the living tribunal and the one above all - were they formed from the infinity stones ?
Nemesis was the single being in existence. She created the multiverse when she shattered herself, and split into the infinity gems, the six singularities mentioned by the collector. This is what sparked the multiverse into being.
So, answering the question, they did exist as a single being, not separate entities before the multiverses were sparked into creation.
We know that nemesis is less powerful than TOAA because the full infinity gauntlet is nothing next to him. It would be probably impossible to create a being more powerful than yourself, Nemesis could not have created TOAA. He is meant to have created the entire multiverse, which I think includes her. As for him, I think he has no origin and always was and just decided to create the multiverse. As I understand it, he created all other cosmic beings to do their desired effects on the universe for him e.g Galactus was there to balance eternity with death.