sounds to me like maybe the system got bugged, it happens to me a lot, I'm not sure how to fix it and i dont know if there's a way to fix it, if you can just ignore the upgrade buttons and try to use it as normal, maybe as time goes on brainly will release an update which may trigger your account and it will straighten itself out
as for the consequences I dont see anything wrong with it, really its like having a family computer for your home but as an online account, I think what your doing is great, the fact that your sharing your account is just as fantastic, I would say keep on trucking and hope maybe the issue will resolve itself
if it starts acting like you dont have a plus account when you know that you've bought it, maybe contact brainly and see if there's anything they can do, who knows, maybe they can get the upgrade buttons out of your face wile they're at it
I wish ya luck with it and hope things get straightened out for ya, keep it real and stay safe
