So if you had a City, a Town, and an Explorer all with Strife, the Town + Explorer could destroy the City while the City destroyed the Town + Explorer.
Damage from a single effect is done simultaneously. For instance, with the threshold effect of Dissolve the Bonds of Kinship, a City, a Town, and 5 Explorers can wipe each other out.
Both Serene Waters and Roiling Waters can only be claimed as a first Healing Card, and both Waters Renew and Waters Taste of Ruin can only be claimed as a final Healing Card.