According to the corleone crime family graphic, Fredo was an Underboss, more powerful then the caporegimes, although it certainly didnt seem it in the film.

And also Tessio was killed just after the massacre, so it unlikely he would have figured in mikes plans

Sonny - Well then, business will have to suffer, all right? And listen, do me a favor, Tom. No more advice on how to patch things up, just help me win, please