Round table

Hello, esteemed players!
At the beginning of the battle, I had 3+3 Archangels. By the end, I had 1+2 Archangels left. Neither the group with 1 Archangel nor the group with 2 Archangels could resurrect the adjacent Archangel (the Archangel doesn't have enough power to resurrect another Archangel). Then, the same thing happened with Hydras – 1 Archangel couldn't resurrect a fallen Hydra.
My question is: what criteria are needed for an Archangel to be able to resurrect, and who can it resurrect?