Ok, I have now found the solution and, I have to say, was extremely easy. I write if someone else has the same problem.
Finally I've solved with Flash Media Live Encoder. You have to create 4 (in my case) video objects in your webpage like below, changing localhost for your hostname.
<object width='640' height='377' id='StrobeMediaPlayback' name='StrobeMediaPlayback' type='application/x-shockwave-flash' classid='clsid:d27cdb6e-ae6d-11cf-96b8-444553540000'>
<param name='movie' value='swfs/StrobeMediaPlayback.swf' />
<param name='quality' value='high' />
<param name='bgcolor' value='#000000' />
<param name='allowfullscreen' value='true' />
<param name='flashvars' value='&src=rtmp://localhost/live/livestream&autoHideControlBar=true&streamType=live&autoPlay=true' />
<embed src='swfs/StrobeMediaPlayback.swf' width='640' height='377' id='StrobeMediaPlayback' quality='high' bgcolor='#000000' name='StrobeMediaPlayback' allowfullscreen='true' pluginspage='http://www.adobe.com/go/getflashplayer' flashvars='&src=rtmp://localhost/live/livestream&autoHideControlBar=true&streamType=live&autoPlay=true' type='application/x-shockwave-flash'> </embed>
</object>
As you can see, by default the stream name is "livestream", you have to change for every object to be different. Ensure "live" folder is created (when you install FMS in localhost by default creates this folder, but in influxis you have to create manually).
Every video publisher has to open Flash Media Live Encoder and change the Output value of "Stream" by the value of stream name of the respective video object.
That's it! Works perfectly, great resolution and great performance, better than expected. Hope it helps!