You can have up to two animal companions active at once.
Uncommon
Archetype
Feat type
Archetype Feat
Level
16
Traits
Uncommon, Archetype
Prerequisites
Mature Beastmaster Companion, you have multiple animal companions
You can have up to two animal companions active at once. However, when you do, it's slightly more difficult to Command them. If you don't Command either of your companions, one of the two (your choice) can still use 1 action on your turn to Stride or Strike, per Mature Beastmaster Companion, but not both. When you Command an Animal, either choose one of the companions to take 2 actions, as normal, or else each companion can take 1 action to Stride or Strike. Either way, you can't Command an Animal to make either companion act again until your next turn. Beastmaster Focus Spells
Source: Pathfinder Player Core 2, p. 189
Bring Lead the Pack into a Pathfinder 2e game with The DM Screen.