The Lion King 2: Simba Pride is a 1998 animated film. It takes place after the events of the first movie.
Zira's absence in the first movie[]
At the end of The Lion King, Zira and her lionesses are nowhere to be seen during the fight or after that event. Most likely because they were loyal to Scar, and they were searching for food at the time that Simba came back and overthrew him. By the time she came back, Scar was dead and they were pretty pissed about it, causing them to be banished from the Pridelands.
Kopa[]
Kopa was the original prince and future King of Pride Rock, before Kiara was born. (Note that I don't consider The Lion Guard to be canon, because the series does not make any sense and it was only adapted to be on Disney Junior.) Every book published before the release of Simba's pride states that the baby being held by Rafiki at the end is Simba and Nala's son. This is obviously not Kiara, because at the start of the second movie, her presentation is way different from Kopa's. This leads us to the question "Why don't we see him in Simba's Pride?" The reason why is because he was possibly killed by Zira or another lioness loyal to Scar. You see, Zira claimed that Kovu was the original heir to the throne when Scar ruled the Pridelands. Kopa being born threw off Kovu, and Kopa was killed by Zira or another lioness (that was loyal to Scar) out of anger. This is why Simba banished them to the Out lands.