How many people are allowed by the stack exchange community to control one stack exchange community? Is is allowed that one account can be controlled by more than one people and is it allowed for one person to keep more than one community (maybe different accounts for different stack exchange communities)?
Yes, it is permitted to keep different accounts for different communities. The only real rule about multiple accounts is that they cannot be used to give the impression of more than one person. For example, you can't vote with two accounts on the same question, have a conversation with yourself as if you are two unrelated people, use one account while another is suspended, etc. Apart from that, you can even have multiple accounts on the same community - as long as there is no abuse of the system.
The main challenge to having multiple accounts is the single log-in system. When you log in to one StackExchange community, you are automatically logged in to other communities. So, to use multiple accounts, you must intentionally log out and log back in, or use a separate browser. It used to be that you could log in to different communities as different users at the same time in the same browser instance, but StackExchange announced recently that this was never intentional and that their updated single sign-on does not support it.
one account can be controlled by more than one people
Apparently, this would be against the Stack Exchange Terms of Service, which state
- Access to the Services
Subject to the terms and conditions of this Agreement, Stack Exchange may offer to provide the Services, as described more fully on the Network, and which are selected by Subscriber, solely for Subscriber’s own use, and not for the use or benefit of any third party. [...]
Subscriber certifies to Stack Exchange that Subscriber is an individual (i.e., not a corporate entity) at least 13 years of age.
On one hand, this implies that one is unlikely to get a explicit permission to use an account by a group.
On another hand, the Terms of Service are not exactly what drives day-to-day moderator activities. The ToS are an agreement between user and Stack Exchange, Inc., and moderators are not representatives or agents of Stack Exchange. If they decide to take an action against a group account, that would probably be based on what that account does, not on what the Terms of Service say.