Hi Tridip,
There are no permissions associated with Chat. Chat is turned off or on at the Auction Type level. If it's turned on, it's on for all collaborators on the Auction.
There are permissions associated with Discussions. If you go to Security in Setup, you'll see that there are ACLs for Discussions in the Business Documents section.
Typically, the number of collaborators added to an Auction is limited to those running the Auction. If there are many stakeholders that have an interest, then often those running the Auction will schedule a conference room and project the Auction so everyone can see but they are not given access. Is this an option for you?
I hope this helps some,
Rosemary