I am making an app and Kinvey will be used so users can sync their data with their other devices as well as other specific people (family members, etc).

In both of those cases, the quickest and most painless way for a user to accomplish that would be for all the other devices and users to simply sign in under the same Kinvey account. That way, all they have to do is sign in and the data will sync automatically. Otherwise, they would have to signup for multiple accounts and manually grant access to the other accounts using the AccessControlList. 

Now with the first option, from what I understand, it would only result in 1 Kinvey account and hence one active user even though multiple people are actually using Kinvey. What is the policy regarding that? If multiple people using a single Kinvey acc is not allowed, how about the same person but with multiple devices? And if multiple people using a single Kinvey Acc is allowed, theoretically, what is stopping me from signing in all my users under one single Kinvey Acc and having a separate column that indicates which entity belongs to which user? That way even if I had 100 mil users, I would still be able to stay under 100 active users but still tax Kinvey's servers with 100 mil users' requests.

No worries, please let me know if you have any other questions,

Yes that makes sense. Thanks.

There is nothing stopping you from doing that, but we do monitor user account activity.  If we feel as though you are violating the terms of service we can lockdown your application without warning.   Use of service accounts or allowing sync of a single account across multiple devices is totally allowed within reason.   There is no arbitrary amount of devices where we say "that's the limit", but it would be pretty clear if someone was abusing it.   The average user on Kinvey has 1-2 devices paired with their account, which is reasonable.

If an app had 1000 users but each user had 5 - 50 devices, we would be extremely skeptical that they weren't in violation of the TOS.

Does this make sense?   

Okay, thanks. 

It seems like your response ended prematurely?

Also, if multiple people using a single Kinvey Acc is allowed, theoretically, what is stopping me from signing in all my users under one single Kinvey Acc and having a separate column that indicates which entity belongs to which user? That way even if I had 1 billion users, I would still be able to stay under 100 active users but still tax Kinvey's servers with 1 billion users' requests.

Yes,

This is allowed and used quite widely.   This is also possible via OAuth / SSO/ Social Auth providers as well.

There would need to be some sync code executed by the client once you set up a new 

Thanks,

To be clear, the most important thing is the convenience rather than having fewer active users.