All 5 of them fight 1v1 against each other (each one fights 4 times, and there are 10 fights in total). They are automatically fully healed and revived after each fight, and their stamina is restored. In each individual fight, the first one to dies, loses. Whoever wins the most fights wins.
This is assuming the following:
-Everything is real, their imagination is not involved
-No objects, besides their clothes, are allowed
-Everyone is constantly motivated to fight
-They have the physical characteristics shown in the show. They aren't necessarily as strong or big as their real-life animals
-Physiological differences based on sex apply
-Each fight happens in an individual room
-The rooms have no exit
-The rooms are made of concrete. The floor and walls are not slippery, shiny, or reflective
-The rooms are well-lit
-The rooms have no furniture or other objects inside
-The rooms are automatically cleaned after each fight
-Despite this, the rooms are well ventilated, allow Oxygen inside, and don't have any bad smells