Who is the PRIMARY person on the ISP account, and who owns the network hardware? That person should be in charge of making sure everyone is getting equal use of the internet... If the others are merely downloading, ask them to do that at night when no one is using the bandwidth.
As far as NetCut, I am not at all familiar with the software, but it looks as though it can be used for DOS attacks (by ARP Spoofing) WITHIN the LAN, which you might be experiencing...
ARP spoofing - Wikipedia, the free encyclopedia
Google is your friend.......
anti netcut - Google Search