If it's only showing your household IP, it had to be you. How do you know somebody logged into your account? It could have been a tablet or phone email app triggering a sign in event, but if they're all devices on your IP I don't see why they'd trigger anything.

it was a mac computer but no one in my household has a mac

Have you pissed off anybody?
They may be out to get you

Meh, it could be because someone logged onto a device that uses IOS I guess, I know that part of it's os identifier is mac.

KrazeVI wrote A couple minutes ago someone logged into my gmail account and when I checked the device it had the same ip address as all the devices in my household. it wasn't anybody in my house or on my router so my question is why do they have the same ip address as my devices

Welcome to the scene see that you host lobbies many people are messed up and you need to be careful dont add random people on skype, aim, and etc. Just people suck so be careful who you add and become buddies with never know. Have ran into many situations that have same complications your having.

Well GoodLuck

I already changed my password and added the 2step verification, is there any thing else I can do

Another question how did they get the same ip as me ?

KrazeVI wrote Another question how did they get the same ip as me ?

The IP address is assigned to your household, as networks can't have two of the same IP addresses without having issues.

They could have spoofed the address, but that is highly unlikely.