BLE device can avoid broadcast conflicts?

I'm developing a simple game with 10 BLE(DA14531) and 1 PC, actually the BLE devices should not be limited, it can be increased I hope.

As I posted before,the TBluetoothLE component of Delphi IDE did not provide information on how many BLE can be managed at the same time.

Usually the first 7 BLEs can be connected soon, and later ones(8/9/10) getting harder and harder to response to scan & require services,and last 2 or 1 BLE may never connect,and this is not limited to some one, they can be connected soon with cold restart(all 10). 

There are many questions I did not find answer,one question is :

Is it possible that more than 1 BLE send ADV packet at the same time?

If so,they will adopt some strategy to avoid conflict?

Thank you.