Not as far as I know (at least not savely). The only thing definitely related to the user behind a stream is the given user_id.
You can collect those from your first request and create a second one using the users endpoint with id=firstId&id=secondId etc.
What you can try as well eventhough I don’t know how safe that is (regarding the correctness of the outcome) would be to read the thumbnail_url field which ends in the following (at least in the examples and a test request I made):
live_user_<USERNAME>-{width}x{height}.jpg
parsing this with something like .split(/[_-]/)[2] should get you the login of the user.
Again though I don’t know whether that will always stay like that nor whether that will always be kept in that format.