If I cast betray in the elmental master's magnus, does the transfer pain works? If so, the damage that the master takes is again divided in 2

Betray is a spell u can use on other servitors/summons and pets, but i am not sure about the pets, and it makes them attack thir master.
Transfer pain - dunno if half the dmg but anyway some serios dmg is transfered to the servitor, including dmg taken from a betrayed servitor, ANY dmg that u take is shared with ur servitor.

higher level of transfer pain transfer 50% of damages you receive on your summon
so if a summoner receive betray on his summon, his summon will hit him so the summon will "damage himself" due to transfer pain.
btw u can't cast betray on your summon.