From what I could find in the rules the answer is no. But I am curious if familiars that are treated as heroes like Brightblaze can open doors or not.

Also, does it use an action of Challara to use Brightblaze? Or does he just get his own separate action on top of Challara's normal actions?

During that action can he move and attack once? On the card it just says he can attack, but he has a speed value, so I assume he can move once also.

Opening a door takes an action so unless the familiar is specifically granted with that ability can't open doors.

It doesn't take an action away from the hero to activate a familiar. The hero can either activate the familiar before taking any actions or after taking all of her actions.

A familiar can perform a move action when activated and then may perform other actions granted by either their card or possibly skills that the hero it is attached to has learned.

Opening a door takes an action so unless the familiar is specifically granted with that ability can't open doors.

It doesn't take an action away from the hero to activate a familiar. The hero can either activate the familiar before taking any actions or after taking all of her actions.

A familiar can perform a move action when activated and then may perform other actions granted by either their card or possibly skills that the hero it is attached to has learned.

Awesome, thanks for clearing it up for me.