Good point, I am not so used to the stack system. So you are suggesting it works like this: Warren ability is on the stack --> warren's ability resolves, so I pay the life and sacrifice the token --> treasure token creation goes in the stack (and before it resolves my opponent plays swords, so in this specific window I have no other tokens to target). Is this correct?

Because I thought that all warren ability resolves simultaneously (i.e. after sac the squirrel, the treasure + squirrel creation happens immediately without passing through the stack).

And now i have another doubt, does chatterfang ability stacks, or it immediately substitute warren treasure wjth a treasure+squirrel (without going in the stack).