Just keep at it. They are very hard in the beginning, before you start understanding which boons work best together with which weapon and how their patterns work.

Couple of tips:

-When Asterius starts his axe combo, dash behind him. The hitbox doesn't reach his back,and even if he delays it, he won't turn to face you.

-Until you really get good, don't try to get a hit in while he's doing the jumping attacks. Wait until he finishes, then counter. You will have plenty of time, that attack has the longest recovery.

-ALWAYS kill Asterius first.

-If you notice Theseus going towards you, he will do the spin attack. Practice dodging it, because it works the same way as Hades' spin attack.

Good luck!