At my airline it calls for the Captain the take control of the aircraft in emergency, however it is up to captain to choose when this is appropriate.
We drill for the PF to intiate engine shut down.
E.g. Fire bell after V1:
P.F: (at or above 600ft) Call for 'Engine Fire/Separtion recall items'
and then proceeds to close throttles; Disconnect AT; Start Lever to Idle Cut-off... All actions confirmed by PNF. After this is completed PF calls for continuation of recall items, which is carried out by the PNF.
Sorry got to run, will add more later!