Pyreheart Wolf has a triggered ability that makes it harder for your opponent’s to block your attacking creatures. When Pyreheart Wolf attacks, its ability triggers. When this triggered ability resolves, it creates an effect that prevents your attacking creatures from being blocked by just one creature.

This ability is not cumulative in any way. If two Pyreheart Wolves attack, both of their abilities will trigger and resolve independently. However, these two abilities to not create an increased effect. Both of these effects will end up doing the exact same thing, and prevent your attacking creatures from being blocked by just one creature. As long as the defending player assigns two blockers to an attacker, neither one of these restrictions is being violated, so the block is legal.