Responses
Isn't the other dragon Cardinal Brixton, considering the silhouette around the start of season 2
It is, but OP's point is that we haven't seen Cardinal Brixton interacting with Brian during the flashback yet.
I am now sure that Ian and Brian are two different personalities. Ian may be the reincarnation of Brian but that was his past life, Ian is his own person.
We have yet to meet the other dragon (i forgot his name) and know why he is obsessed with Brian. I really thought that both of them would meet Brian at the same time but I guess that is not what happened. So, the conflict of the brothers started with Brian's death.