To complete the answer of imlokesh, here is the description of Twitter concerning the UserStream.
Minimize the number of connections your application makes to User Streams. Each Twitter account is limited to only a few simultaneous User Streams connections per OAuth application, regardless of IP. Once the per-application limit is exceeded, the oldest connection will be terminated. An account logging in from too many instances of the same OAuth application will cycle connections as the application instances reconnect and disconnect each other.
So you can have multiple UserStream running for one application but their number will be adding up regardless of their ip.
Therefore you will not have any choice other than having multiple applications.
Please both of you note that this is not "authorized" by Twitter and this can result in having your applications shutdown (which happened to me once 2 years ago).
Linvi
Minimize the number of connections your application makes to User Streams. Each Twitter account is limited to only a few simultaneous User Streams connections per OAuth application, regardless of IP. Once the per-application limit is exceeded, the oldest connection will be terminated. An account logging in from too many instances of the same OAuth application will cycle connections as the application instances reconnect and disconnect each other.
So you can have multiple UserStream running for one application but their number will be adding up regardless of their ip.
Therefore you will not have any choice other than having multiple applications.
Please both of you note that this is not "authorized" by Twitter and this can result in having your applications shutdown (which happened to me once 2 years ago).
Linvi