If two phones use the same google account, can I log in while other person is already playing ? Is the other person kicked out?
Yes you can and none is kicked out.
I have configured it currently on both of my Android phones. The data is saved on the server, and syncs after some time in cases where you catch a Pokemon on one phone. No data is saved locally except your login info.
I have never tried giving one of the phone to another person and access the game at different location with same google account. That might bring down a Ban situation.
My son and i use the same account on different phones. we can't both collect pokestops at the same location but he can use it at one location while i use it at another at the same time. anything i catch appears in the caught pokemon on hos phone and vice versa. Same with pokeballs and items collected from pokestops.
Me and the wife both have the same account on the phone. while shes is park and grabbing pokestop farm i walk around to grab further pokestop. The items are shared and if one of us catch a pokemon the other wont be able to catch the same. its a great team effort in a way.
you also cant flip the same pokestop. so there is not really abuse because someone has to walk/move and you cant double dip on anything.