Streaming HD video or audio without dropped connections require a constant supply of bandwidth sufficient for the demand. If you are experiencing any drop outs and you have open WiFi in the hall, then it is possible when the friends enter the hall with their cell phones, and devices - they are automatically connecting to that WiFi. All their pictures automatically start uploading and downloading to and from Dropbox, One Drive, iCloud, etc. This can cause disconnecting or buffering. The router is doing its best to share the available bandwidth between the demand of all devices, not really considering which is “more important”.
The Quality of Service feature on your router lets you prioritize the things that are most important. With good QoS rules, you can ensure that your streaming doesn’t stutter or cut out because a large file is downloaded or uploaded at the same time. Refer to your router manual to give priority to the IP address or the MAC address(s) of your streaming devices. Reserve the amount of bandwidth you stream at for the device streaming.