I'm no sure of the stability too, even if it should be better than the my original sketch.
The problem I see is for the kickstand in portrait mode: the junction is not in the middle. So either the kickstand is in the low part of the tablet and the stability is not good in almost flat, or the kickstand is in the upper part and the tablet cannot stand almost vertically.
Or we can build the two kickstands with the junction in the middle, but in this last case the tablet will no have a good stability in one side on both portrait and landscape.
I think if we want a double kickstand, we will be stuck trying to solve the problem if we just imagine kickstand as a plate.
We need to consider other kind of kickstand.
I'm not a fan of the kickstand from the hp specter 12 X2 (surface-like), but this kind of kickstand allow to build two kickstands in a easier way.
Here an idea for two kickstands with the hp-like kickstand:
Line-kickstand allow us far more possibilities in design, here some ideas to help your imagination:
Looking forward to see your ideas!