Amos didn't interfere earlier since he wanted Anthony to kill Zara and Clara, therefore also tiring himself out in the process.
So then he could swoop in and kill the half dead Anthony and reap the rewards.
But right from the start, he could see how Anthony toyed with Zara and Clara.
If Zara and Clara died, it didn't make any difference to Anthony since Anthony toyed with them, so he decided to interfere and save them so they could work together and reduce the pressure he would receive when facing Anthony.
Amos gave potions he already took out from his space rings to Clara and Zara and allowed them to heal their injuries.
Since Anthony sealed their space rings somehow, he decided to take out his potions from his space rings before Anthony seals his off like he did to the sisters.
Anthony just stood there watching as both sisters healed, their skins moving and healing at a rapid pace.
