You beat all of them at level 1. Renek is closer than the other 2, but you still should be able to beat him if he starts Q.

You beat Nasus until he hits 6 and has Sheen, unless you're already far enough ahead to just beat him at this point, he'll run you down with R and wither and Q you to death pretty easily.

Renekton will beat you at level 3+ unless you have lane control from level 1 and haven't let him build Rage while trying to keep his hp down with trades when possible. Shield the stun since it's most of his damage (if empowered), punish his long W and E cooldowns. Aftershock isn't terrible here if you want to be safer.

Teemo, you can actually just run at him and beat him level 1, if you have ignite you'll either burn his flash or kill him. If you don't have ignite then you still win the trade by a ton unless he goes blind first. After that, you want to bait out his blind and shield it. You beat him at level 6+ with an all-in, just don't run into shrooms, take sweeper if you have to, or buy pinks. Take electrocute and proc it whenever his blind is down, if you have an advantage, you can just get hit by his blind in an all-in and still beat him.