That is correct, you send to a user not an email address.
It also dedupes email in a campaigns, so even if there are multiple users with the same email address, only 1 email is sent which could also be problematic depending on your message purpose and needs.
The best practice is to have email unique per user, but it seems that won't work for you.
The duplicate users (multiple users with the same email address) are they different types of users / services? If so, you could split into different apps/workspaces
Another option would be to send triggering events to a braze endpoint to send the messages.
Alternatively, in this case: User A and User B qualifies for Campaign 2
You add a custom attribute when sent to the use record and loop the sending checking for the attribute.
