You have two nice Pleiospilos nelii . The one on the left is var. rubra.
My avitar is a blooming Pleiospilos nelii var. rubra.
These plants do like filtered sunlight, not direct outdoor sun.
As Baja mentioned the window does naturally filter some light.
These plants do like it more on the dry side.
I have killed too many of them by over-watering.
Mine do best when I grow them in small pots.
The outer leaves do normally shrivel up and turn crisp.
