I have had these windows in my LEGO collection since the 80's and my mum bought them second hand. They look and feel like Lego but don't have the word LEGO stamped inside the hollow circles on top.
These look like "Blue-Box" , a construction toy from Singapore
- Blue Box basic elements with a 2X4 LEGO brick on the right
- The inside of a "Blue-Box" construction set
I don't think so; I've seen a lot of old Lego, and I'm fairly sure I've never seen these before.
BrickLink has a window category, and none of the pieces in there match.