Sub-site's register process on multisite environment

Hello
I hope you having a good day.
I am now learning the behavior of multisite environment ( subdirectory)

I activated CoursePress Pro on 2 sub sites(SiteA and SiteB).
And, one subscriber registered to SiteA, then the subscriber tried to register SiteB too. However, the subscriber has already had an account on SiteA, so the subscriber could login to the SiteB without registration. ( I realized, when the subscriber registered SiteA, he automatically registered to my main Site's Buddy Press. I don't hope, if possible.)
Furthermore, to take a look more, I tried to check if the subscriber work correctly on both SiteA and SiteB. Of course, the subscriber could work on Site A, because he has signed up for Site A, but in terms of SiteB, some features didn't work correctly (probably) due to that he hasn't signed up for SiteB.

So, I realized that it seems that there are some features which I don't hope.

That's why I am considering make next feature work.
1: The subscriber(user) is required to register for each sub-site. = Even if the subscriber make a register for SiteA, he can't register Site B with the account.
2:I realized, when the subscriber registered SiteA, he automatically registered to my main Site's Buddy Press. I don't hope, if possible.

I know this is really hard question, but could you help me ?
If you need, I will give you further information.

King Regards
KAZUKI KIKUCHI