In Freshchat, you can use a single instance(account) across multiple websites. To do so, you have to declare a unique siteID for each of these website while adding the Freshchat widget code to the websites. When users ping you from these websites, each conversation/user from the different websites will be treated as a different user/conversation. Whereas, pages/sites with the same siteID will have common users/conversations.
For more information on how to declare siteID, visit Freshchat developer’s portal: