If you are organizing your prisons properly, this is not an issue. Inmates who are sentenced for serious crimes like gang stuff should never be able to communicate with each others without supervision. They are people who really like to abuse all kind of weakness and kindness shown to them, so I don't feel sad if they have really bad and lone time in prison. Things like prison gangs are so stupid and easily preventable if you don't let inmates "socialize" with each others all the time.
Prisons run on taxpayers money, and its really not cheap thing. And its not like they magically turn into taxpaying members of society after they get released.
I think, No matter what their home country says, they can have em back. We should not care what happens next, since they themselves fucked up bad enough after given second chance.
Doesn't matter what their country is doing, they get locked up and sentenced.