What level should you be at (roughly) to take on each boss?

1 - Zoe and Grizzbolt - 30,550 HP

2 - Lily and Lyleen - 69,375 HP

3 - Axel and Orserk - 130,700 HP

4 - Marcus and Faleris - 146,975 HP

5 - Victor and Shadowbeak - 200,750 HP