How can I check which user has how many referrals and who they have referred?
Yes, but it only shows the number. How can I see who are the members that they referred?
I don't believe there are graphs for that yet. I might be wrong though.
I'm currently working on a plugin that incorporates a better referral system like that, it might not be available for everyone, but if my client lets me release it I will
(won't be free however)
You can use the ACP to see who someone has referred. Just go to Users & Groups > User Option > Show Referred Users
It's tedious if you want to see who everyone's referred, but I believe that's the only way to do it at this point.
Might be something at MyBB Source or MyBB Central.
mybbsource valid referrals plugin