Cannot share via AirDrop between iPhone simply by not discoverable by each other even though AirDrop is turned on on both iPhone
It's happening to my cousin's iPhones.
When I tried to share photos via AirDrop, my cousin's iPhone simply not discoverable by my iPhone even though AirDrop was turned on on both iPhones and set to everyone, bluetooth and wifi also turned on but my iPhone seemed cannot see my cousin's iPhone. This also happen when they tried to share anything via AirDrop to other iPhone (their iPhone cannot see other iPhone).
Funny thing is, my cousin's iPhone can share via AirDrop to each other iPhone and only to each other.
It's hard to explains with words so here it is:
A: cousin A's iPhone (iPhone 5s)
B: cousin B's iPhone (iPhone 5s)
C: my iPhone (iPhone 6s)
D: any other iPhone (iPhone 5, 6+, 6s)
A discoverable by B (can received and send via AirDrop)
B discoverable by A (can received and send via AirDrop)
A and B not discoverable by C and D (therefore cannot received and send via AirDrop)
C and D not discoverable by A and B (therefore cannot received and send via AirDrop)
It is weird that their iPhone only work for each other. What possibly caused this? this is my first time to see something like this.
PS: I've done restarting both iPhones and even my own iPhone, turned on and off again AirDrop, bluetooth, wifi, set AirDrop setting to everyone back and forth.
iPhone 6s, iOS 9.3.1


