I don't care it's your brother, sister, nephew, uncle, grandmother, mother, father, child, baby, son, grandfather, friend, girlfriend, boyfriend etc. If there's 2 accounts or more caught using same address/social media and joining in the same campaign, it's cheating and should be tagged.
Frankly, this is why I gave up tagging cases like this a long time ago--there's just too much doubt in my mind as to whether it's true or not. There are apparently valid reasons why someone might share a payout address, though I don't see any reason why two people should have the same social media account.
That's my opinion, however. Other DT and non-DT members are free to take a zero tolerance policy in situations like this. I sure as hell wouldn't oppose a neg...but I'd be careful, too.