Trusova is guaranteed two - one because she is 5th on the season's best list, and one because she is 24th on WS list (shows you how hard it is to get on top of the WS as a junior)
Kostornaya and Shcherbakova are each technically only guaranteed one from being on the SB list. However, I couldn't imagine them getting only one. I can't remember anyone having as much success in juniors as them and not getting two GPs. And I'm sure RusFed will want them to have two, so they'll pull whatever strings they have to. In the rules it does say that the JGPF champion and Junior Worlds medalists are taken into account when assigning GPs, so hopefully that will help, although it still doesn't guarantee them a second one. I hope Russia does the smart thing and doesn't submit Sotskova, no offense to her, but those GP spots would be much better given to Gubanova or Tarusina

pray

. (and poor Tarakanova isn't even close to getting one, even though in any other country she would've been able to

).