Should I add a "S" at the end of these names in this sentence?

[alishababy]

Members of Peter, John and Ian's gang were responsible for the robbery.

or

Members of Peter's, John's and Ian's gang were responsible for the robbery.

 

[emsr2d2]

Use the first.

 

[Barb_D]

If you want to research this feature, use the search term "coordinated possession."

 

[Lynxear]

I find either sentence awkward. putting the possessive on just one member implies that that person is the leader and the second sentence just looks weird to me.

A better sentence would be:

The gang made up of Peter, John and Ian was responsible for the robbery.

 

[emsr2d2]

I didn't take the original to mean that Peter, John and Ian were the only members of the gang. I took it to mean that some/all members of a gang of which Peter, John and Ian were considered to be the main members (possibly the leaders) carried out the robbery. The three men named might not even have taken part in it themselves.