Let's start with the obligatory illustration! (cobbled together quickly because I was forgetting it)

(I know, Ami has actually never been a PPC agent, but I felt like having a Nikki and Ami illustration this time)

As for what they are doing, I have to break it down by timeline.

In the main timeline, I think it is pretty likely Sergio and Nikki invite Corolla over, alongside Sergio's only surviving relatives (Colonel Johnson, his grandfather, and Virgilia, his aunt). Quite likely they also invite Aya and Kuroko over - aftert all, they're honorary aunts to Keiko too.

In the TWWA timeline... it's a bit of spoilers, but I can say it is a much bigger family reunion!