You’re forgetting about Arquiusprite which is Dirk’s sprite. 

The Beta kids didn’t decide the time period the Alpha kids were sent back, it was Skaia who decided what portals to send them through. 

It was popular humanized AR in the fandom that worked it’s way into one flash.

The kernelsprites belong the the Alpha kids. In the post-retcon timeline Tavris, Fefeta, and Erisol sprites were never prototyped so there were 3 empty ones. Vriska prototyped Tavros in one of them so now there’s Tavrosprite, Jaspersprite prototyped dead pre-retcon Rose and himself in another, and the third one is still empty but it probably won’t be for much longer.

They did have a reckoning.

Typheus knew another John from the pre retcon time line would bring his Lowas with him into the post retcon timeline. Also, Jade spending three years by herself without John or Davesprite was the price Typheus warned would happen. Because John was able to edit the timeline himself his friends had to feel the same loss he did. 

Because they are the product of two sprites merging together. 

Yes, she was killed by Gamzee.

They all died long before she entered her session.

Here.