If the IP is the only indicator that it can MAYBE be a cheater, you should not.
As long all 3 accounts are active and the members make their clicks, they are YOUR active members!
It's up on the ISP-service, but with some you have always different IP's like at AOL or like i have with my DSL-connection (I'm only not really in danger to be called a cheater, cuz in this gptre-business are not that many german DSL-User

)
If all 3 accounts are showing something else , what lets you think, it's a cheater like same password or same way how the email-adresses are builded or something like that, you can maybe think about, to delete them.
Me i would not delete accounts when they earned some cash and are still active ...(they also earned it for the upline and the whole program!).
Greetz, Heike