603.6a. Enters-the-battlefield abilities trigger when a permanent enters the battlefield. These are written, "When [this object] enters the battlefield, . . . " or "Whenever a [type] enters the battlefield, . . ." Each time an event puts one or more permanents onto the battlefield, all permanents on the battlefield (including the newcomers) are checked for any enters-the-battlefield triggers that match the event.

116.5. Each time a player would get priority, the game first performs all applicable state-based actions as a single event (see rule 704, "State-Based Actions"), then repeats this process until no state-based actions are performed. Then triggered abilities are put on the stack (see rule 603, "Handling Triggered Abilities"). These steps repeat in order until no further state-based actions are performed and no abilities trigger. Then the player who would have received priority does so.

402.6. Once activated or triggered, an ability exists independently ofits source as an ability on the stack. Destruction or removal of thesource after that time won't affect the ability. Note that someabilities cause a source to do something (for example, "ProdigalSorcerer deals 1 damage to target creature or player" ) rather than the
ability doing anything directly. In these cases, any activated ortriggered ability that references information about the source willcheck that information when the ability resolves, or will use thesource's last known information if it's no longer in play.