texture assigned to the window

If I open a second window - can I use the same textures in it as in the first or do I have to reload them and assign them to the new window?

the textures are freed when you destroy the renderer. But the renderer depends on your window; Hence it is safer not to use the same texture in two windows. However if you are sure that you destroy both renderers at the same time, it could work maybe, I have not tried.